The Tor Browser: media/libpng/pngrtran.c@97036ab72558 (annotated)

media/libpng/pngrtran.c@97036ab72558 (annotated)

media/libpng/pngrtran.c

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* pngrtran.c - transforms the data in a row for PNG readers
  *
  * Last changed in libpng 1.6.10 [March 6, 2014]
  * Copyright (c) 1998-2014 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
  * and license in png.h
  *
  * This file contains functions optionally called by an application
  * in order to tell libpng how to handle data when reading a PNG.
  * Transformations that are used in both reading and writing are
  * in pngtrans.c.
  */
 #include "pngpriv.h"
 #ifdef PNG_READ_SUPPORTED
 /* Set the action on getting a CRC error for an ancillary or critical chunk. */
 void PNGAPI
 png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
 {
    png_debug(1, "in png_set_crc_action");
    if (png_ptr == NULL)
       return;
    /* Tell libpng how we react to CRC errors in critical chunks */
    switch (crit_action)
    {
       case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
          break;
       case PNG_CRC_WARN_USE:                               /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
          break;
       case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                            PNG_FLAG_CRC_CRITICAL_IGNORE;
          break;
       case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
          png_warning(png_ptr,
             "Can't discard critical data on CRC error");
       case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
       case PNG_CRC_DEFAULT:
       default:
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          break;
    }
    /* Tell libpng how we react to CRC errors in ancillary chunks */
    switch (ancil_action)
    {
       case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
          break;
       case PNG_CRC_WARN_USE:                              /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
          break;
       case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                            PNG_FLAG_CRC_ANCILLARY_NOWARN;
          break;
       case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
          break;
       case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */
       case PNG_CRC_DEFAULT:
       default:
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          break;
    }
 }
 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
 /* Is it OK to set a transformation now?  Only if png_start_read_image or
  * png_read_update_info have not been called.  It is not necessary for the IHDR
  * to have been read in all cases, the parameter allows for this check too.
  */
 static int
 png_rtran_ok(png_structrp png_ptr, int need_IHDR)
 {
    if (png_ptr != NULL)
    {
       if (png_ptr->flags & PNG_FLAG_ROW_INIT)
          png_app_error(png_ptr,
             "invalid after png_start_read_image or png_read_update_info");
       else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
          png_app_error(png_ptr, "invalid before the PNG header has been read");
       else
       {
          /* Turn on failure to initialize correctly for all transforms. */
          png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
          return 1; /* Ok */
       }
    }
    return 0; /* no png_error possible! */
 }
 #endif
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
 /* Handle alpha and tRNS via a background color */
 void PNGFAPI
 png_set_background_fixed(png_structrp png_ptr,
     png_const_color_16p background_color, int background_gamma_code,
     int need_expand, png_fixed_point background_gamma)
 {
    png_debug(1, "in png_set_background_fixed");
    if (!png_rtran_ok(png_ptr, 0) || background_color == NULL)
       return;
    if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
    {
       png_warning(png_ptr, "Application must supply a known background gamma");
       return;
    }
    png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
    png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
    png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
    png_ptr->background = *background_color;
    png_ptr->background_gamma = background_gamma;
    png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
    if (need_expand)
       png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
    else
       png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
 }
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_background(png_structrp png_ptr,
     png_const_color_16p background_color, int background_gamma_code,
     int need_expand, double background_gamma)
 {
    png_set_background_fixed(png_ptr, background_color, background_gamma_code,
       need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
 }
 #  endif  /* FLOATING_POINT */
 #endif /* READ_BACKGROUND */
 /* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
  * one that pngrtran does first (scale) happens.  This is necessary to allow the
  * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
  */
 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
 void PNGAPI
 png_set_scale_16(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_scale_16");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= PNG_SCALE_16_TO_8;
 }
 #endif
 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
 /* Chop 16-bit depth files to 8-bit depth */
 void PNGAPI
 png_set_strip_16(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_strip_16");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= PNG_16_TO_8;
 }
 #endif
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
 void PNGAPI
 png_set_strip_alpha(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_strip_alpha");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= PNG_STRIP_ALPHA;
 }
 #endif
 #if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
 static png_fixed_point
 translate_gamma_flags(png_structrp png_ptr, png_fixed_point output_gamma,
    int is_screen)
 {
    /* Check for flag values.  The main reason for having the old Mac value as a
     * flag is that it is pretty near impossible to work out what the correct
     * value is from Apple documentation - a working Mac system is needed to
     * discover the value!
     */
    if (output_gamma == PNG_DEFAULT_sRGB ||
       output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
    {
       /* If there is no sRGB support this just sets the gamma to the standard
        * sRGB value.  (This is a side effect of using this function!)
        */
 #     ifdef PNG_READ_sRGB_SUPPORTED
          png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
 #     else
          PNG_UNUSED(png_ptr)
 #     endif
       if (is_screen)
          output_gamma = PNG_GAMMA_sRGB;
       else
          output_gamma = PNG_GAMMA_sRGB_INVERSE;
    }
    else if (output_gamma == PNG_GAMMA_MAC_18 ||
       output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
    {
       if (is_screen)
          output_gamma = PNG_GAMMA_MAC_OLD;
       else
          output_gamma = PNG_GAMMA_MAC_INVERSE;
    }
    return output_gamma;
 }
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 static png_fixed_point
 convert_gamma_value(png_structrp png_ptr, double output_gamma)
 {
    /* The following silently ignores cases where fixed point (times 100,000)
     * gamma values are passed to the floating point API.  This is safe and it
     * means the fixed point constants work just fine with the floating point
     * API.  The alternative would just lead to undetected errors and spurious
     * bug reports.  Negative values fail inside the _fixed API unless they
     * correspond to the flag values.
     */
    if (output_gamma > 0 && output_gamma < 128)
       output_gamma *= PNG_FP_1;
    /* This preserves -1 and -2 exactly: */
    output_gamma = floor(output_gamma + .5);
    if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
       png_fixed_error(png_ptr, "gamma value");
    return (png_fixed_point)output_gamma;
 }
 #  endif
 #endif /* READ_ALPHA_MODE || READ_GAMMA */
 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
 void PNGFAPI
 png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
    png_fixed_point output_gamma)
 {
    int compose = 0;
    png_fixed_point file_gamma;
    png_debug(1, "in png_set_alpha_mode");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
    /* Validate the value to ensure it is in a reasonable range. The value
     * is expected to be 1 or greater, but this range test allows for some
     * viewing correction values.  The intent is to weed out users of this API
     * who use the inverse of the gamma value accidentally!  Since some of these
     * values are reasonable this may have to be changed.
     */
    if (output_gamma < 70000 || output_gamma > 300000)
       png_error(png_ptr, "output gamma out of expected range");
    /* The default file gamma is the inverse of the output gamma; the output
     * gamma may be changed below so get the file value first:
     */
    file_gamma = png_reciprocal(output_gamma);
    /* There are really 8 possibilities here, composed of any combination
     * of:
     *
     *    premultiply the color channels
     *    do not encode non-opaque pixels
     *    encode the alpha as well as the color channels
     *
     * The differences disappear if the input/output ('screen') gamma is 1.0,
     * because then the encoding is a no-op and there is only the choice of
     * premultiplying the color channels or not.
     *
     * png_set_alpha_mode and png_set_background interact because both use
     * png_compose to do the work.  Calling both is only useful when
     * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
     * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
     */
    switch (mode)
    {
       case PNG_ALPHA_PNG:        /* default: png standard */
          /* No compose, but it may be set by png_set_background! */
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
          break;
       case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
          compose = 1;
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
          /* The output is linear: */
          output_gamma = PNG_FP_1;
          break;
       case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
          compose = 1;
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
          /* output_gamma records the encoding of opaque pixels! */
          break;
       case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
          compose = 1;
          png_ptr->transformations |= PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
          break;
       default:
          png_error(png_ptr, "invalid alpha mode");
    }
    /* Only set the default gamma if the file gamma has not been set (this has
     * the side effect that the gamma in a second call to png_set_alpha_mode will
     * be ignored.)
     */
    if (png_ptr->colorspace.gamma == 0)
    {
       png_ptr->colorspace.gamma = file_gamma;
       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
    }
    /* But always set the output gamma: */
    png_ptr->screen_gamma = output_gamma;
    /* Finally, if pre-multiplying, set the background fields to achieve the
     * desired result.
     */
    if (compose)
    {
       /* And obtain alpha pre-multiplication by composing on black: */
       memset(&png_ptr->background, 0, (sizeof png_ptr->background));
       png_ptr->background_gamma = png_ptr->colorspace.gamma; /* just in case */
       png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
       png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
       if (png_ptr->transformations & PNG_COMPOSE)
          png_error(png_ptr,
             "conflicting calls to set alpha mode and background");
       png_ptr->transformations |= PNG_COMPOSE;
    }
 }
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
 {
    png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
       output_gamma));
 }
 #  endif
 #endif
 #ifdef PNG_READ_QUANTIZE_SUPPORTED
 /* Dither file to 8-bit.  Supply a palette, the current number
  * of elements in the palette, the maximum number of elements
  * allowed, and a histogram if possible.  If the current number
  * of colors is greater then the maximum number, the palette will be
  * modified to fit in the maximum number.  "full_quantize" indicates
  * whether we need a quantizing cube set up for RGB images, or if we
  * simply are reducing the number of colors in a paletted image.
  */
 typedef struct png_dsort_struct
 {
    struct png_dsort_struct * next;
    png_byte left;
    png_byte right;
 } png_dsort;
 typedef png_dsort *   png_dsortp;
 typedef png_dsort * * png_dsortpp;
 void PNGAPI
 png_set_quantize(png_structrp png_ptr, png_colorp palette,
     int num_palette, int maximum_colors, png_const_uint_16p histogram,
     int full_quantize)
 {
    png_debug(1, "in png_set_quantize");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= PNG_QUANTIZE;
    if (!full_quantize)
    {
       int i;
       png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
           (png_uint_32)(num_palette * (sizeof (png_byte))));
       for (i = 0; i < num_palette; i++)
          png_ptr->quantize_index[i] = (png_byte)i;
    }
    if (num_palette > maximum_colors)
    {
       if (histogram != NULL)
       {
          /* This is easy enough, just throw out the least used colors.
           * Perhaps not the best solution, but good enough.
           */
          int i;
          /* Initialize an array to sort colors */
          png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
              (png_uint_32)(num_palette * (sizeof (png_byte))));
          /* Initialize the quantize_sort array */
          for (i = 0; i < num_palette; i++)
             png_ptr->quantize_sort[i] = (png_byte)i;
          /* Find the least used palette entries by starting a
           * bubble sort, and running it until we have sorted
           * out enough colors.  Note that we don't care about
           * sorting all the colors, just finding which are
           * least used.
           */
          for (i = num_palette - 1; i >= maximum_colors; i--)
          {
             int done; /* To stop early if the list is pre-sorted */
             int j;
             done = 1;
             for (j = 0; j < i; j++)
             {
                if (histogram[png_ptr->quantize_sort[j]]
                    < histogram[png_ptr->quantize_sort[j + 1]])
                {
                   png_byte t;
                   t = png_ptr->quantize_sort[j];
                   png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
                   png_ptr->quantize_sort[j + 1] = t;
                   done = 0;
                }
             }
             if (done)
                break;
          }
          /* Swap the palette around, and set up a table, if necessary */
          if (full_quantize)
          {
             int j = num_palette;
             /* Put all the useful colors within the max, but don't
              * move the others.
              */
             for (i = 0; i < maximum_colors; i++)
             {
                if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                {
                   do
                      j--;
                   while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
                   palette[i] = palette[j];
                }
             }
          }
          else
          {
             int j = num_palette;
             /* Move all the used colors inside the max limit, and
              * develop a translation table.
              */
             for (i = 0; i < maximum_colors; i++)
             {
                /* Only move the colors we need to */
                if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                {
                   png_color tmp_color;
                   do
                      j--;
                   while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
                   tmp_color = palette[j];
                   palette[j] = palette[i];
                   palette[i] = tmp_color;
                   /* Indicate where the color went */
                   png_ptr->quantize_index[j] = (png_byte)i;
                   png_ptr->quantize_index[i] = (png_byte)j;
                }
             }
             /* Find closest color for those colors we are not using */
             for (i = 0; i < num_palette; i++)
             {
                if ((int)png_ptr->quantize_index[i] >= maximum_colors)
                {
                   int min_d, k, min_k, d_index;
                   /* Find the closest color to one we threw out */
                   d_index = png_ptr->quantize_index[i];
                   min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                   for (k = 1, min_k = 0; k < maximum_colors; k++)
                   {
                      int d;
                      d = PNG_COLOR_DIST(palette[d_index], palette[k]);
                      if (d < min_d)
                      {
                         min_d = d;
                         min_k = k;
                      }
                   }
                   /* Point to closest color */
                   png_ptr->quantize_index[i] = (png_byte)min_k;
                }
             }
          }
          png_free(png_ptr, png_ptr->quantize_sort);
          png_ptr->quantize_sort = NULL;
       }
       else
       {
          /* This is much harder to do simply (and quickly).  Perhaps
           * we need to go through a median cut routine, but those
           * don't always behave themselves with only a few colors
           * as input.  So we will just find the closest two colors,
           * and throw out one of them (chosen somewhat randomly).
           * [We don't understand this at all, so if someone wants to
           *  work on improving it, be our guest - AED, GRP]
           */
          int i;
          int max_d;
          int num_new_palette;
          png_dsortp t;
          png_dsortpp hash;
          t = NULL;
          /* Initialize palette index arrays */
          png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
              (png_uint_32)(num_palette * (sizeof (png_byte))));
          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
              (png_uint_32)(num_palette * (sizeof (png_byte))));
          /* Initialize the sort array */
          for (i = 0; i < num_palette; i++)
          {
             png_ptr->index_to_palette[i] = (png_byte)i;
             png_ptr->palette_to_index[i] = (png_byte)i;
          }
          hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
              (sizeof (png_dsortp))));
          num_new_palette = num_palette;
          /* Initial wild guess at how far apart the farthest pixel
           * pair we will be eliminating will be.  Larger
           * numbers mean more areas will be allocated, Smaller
           * numbers run the risk of not saving enough data, and
           * having to do this all over again.
           *
           * I have not done extensive checking on this number.
           */
          max_d = 96;
          while (num_new_palette > maximum_colors)
          {
             for (i = 0; i < num_new_palette - 1; i++)
             {
                int j;
                for (j = i + 1; j < num_new_palette; j++)
                {
                   int d;
                   d = PNG_COLOR_DIST(palette[i], palette[j]);
                   if (d <= max_d)
                   {
                      t = (png_dsortp)png_malloc_warn(png_ptr,
                          (png_uint_32)(sizeof (png_dsort)));
                      if (t == NULL)
                          break;
                      t->next = hash[d];
                      t->left = (png_byte)i;
                      t->right = (png_byte)j;
                      hash[d] = t;
                   }
                }
                if (t == NULL)
                   break;
             }
             if (t != NULL)
             for (i = 0; i <= max_d; i++)
             {
                if (hash[i] != NULL)
                {
                   png_dsortp p;
                   for (p = hash[i]; p; p = p->next)
                   {
                      if ((int)png_ptr->index_to_palette[p->left]
                          < num_new_palette &&
                          (int)png_ptr->index_to_palette[p->right]
                          < num_new_palette)
                      {
                         int j, next_j;
                         if (num_new_palette & 0x01)
                         {
                            j = p->left;
                            next_j = p->right;
                         }
                         else
                         {
                            j = p->right;
                            next_j = p->left;
                         }
                         num_new_palette--;
                         palette[png_ptr->index_to_palette[j]]
                             = palette[num_new_palette];
                         if (!full_quantize)
                         {
                            int k;
                            for (k = 0; k < num_palette; k++)
                            {
                               if (png_ptr->quantize_index[k] ==
                                   png_ptr->index_to_palette[j])
                                  png_ptr->quantize_index[k] =
                                      png_ptr->index_to_palette[next_j];
                               if ((int)png_ptr->quantize_index[k] ==
                                   num_new_palette)
                                  png_ptr->quantize_index[k] =
                                      png_ptr->index_to_palette[j];
                            }
                         }
                         png_ptr->index_to_palette[png_ptr->palette_to_index
                             [num_new_palette]] = png_ptr->index_to_palette[j];
                         png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
                             = png_ptr->palette_to_index[num_new_palette];
                         png_ptr->index_to_palette[j] =
                             (png_byte)num_new_palette;
                         png_ptr->palette_to_index[num_new_palette] =
                             (png_byte)j;
                      }
                      if (num_new_palette <= maximum_colors)
                         break;
                   }
                   if (num_new_palette <= maximum_colors)
                      break;
                }
             }
             for (i = 0; i < 769; i++)
             {
                if (hash[i] != NULL)
                {
                   png_dsortp p = hash[i];
                   while (p)
                   {
                      t = p->next;
                      png_free(png_ptr, p);
                      p = t;
                   }
                }
                hash[i] = 0;
             }
             max_d += 96;
          }
          png_free(png_ptr, hash);
          png_free(png_ptr, png_ptr->palette_to_index);
          png_free(png_ptr, png_ptr->index_to_palette);
          png_ptr->palette_to_index = NULL;
          png_ptr->index_to_palette = NULL;
       }
       num_palette = maximum_colors;
    }
    if (png_ptr->palette == NULL)
    {
       png_ptr->palette = palette;
    }
    png_ptr->num_palette = (png_uint_16)num_palette;
    if (full_quantize)
    {
       int i;
       png_bytep distance;
       int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
           PNG_QUANTIZE_BLUE_BITS;
       int num_red = (1 << PNG_QUANTIZE_RED_BITS);
       int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
       int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
       png_size_t num_entries = ((png_size_t)1 << total_bits);
       png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
           (png_uint_32)(num_entries * (sizeof (png_byte))));
       distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
           (sizeof (png_byte))));
       memset(distance, 0xff, num_entries * (sizeof (png_byte)));
       for (i = 0; i < num_palette; i++)
       {
          int ir, ig, ib;
          int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
          int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
          int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
          for (ir = 0; ir < num_red; ir++)
          {
             /* int dr = abs(ir - r); */
             int dr = ((ir > r) ? ir - r : r - ir);
             int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
                 PNG_QUANTIZE_GREEN_BITS));
             for (ig = 0; ig < num_green; ig++)
             {
                /* int dg = abs(ig - g); */
                int dg = ((ig > g) ? ig - g : g - ig);
                int dt = dr + dg;
                int dm = ((dr > dg) ? dr : dg);
                int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
                for (ib = 0; ib < num_blue; ib++)
                {
                   int d_index = index_g | ib;
                   /* int db = abs(ib - b); */
                   int db = ((ib > b) ? ib - b : b - ib);
                   int dmax = ((dm > db) ? dm : db);
                   int d = dmax + dt + db;
                   if (d < (int)distance[d_index])
                   {
                      distance[d_index] = (png_byte)d;
                      png_ptr->palette_lookup[d_index] = (png_byte)i;
                   }
                }
             }
          }
       }
       png_free(png_ptr, distance);
    }
 }
 #endif /* PNG_READ_QUANTIZE_SUPPORTED */
 #ifdef PNG_READ_GAMMA_SUPPORTED
 void PNGFAPI
 png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
    png_fixed_point file_gamma)
 {
    png_debug(1, "in png_set_gamma_fixed");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    /* New in libpng-1.5.4 - reserve particular negative values as flags. */
    scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
    file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
    /* Checking the gamma values for being >0 was added in 1.5.4 along with the
     * premultiplied alpha support; this actually hides an undocumented feature
     * of the previous implementation which allowed gamma processing to be
     * disabled in background handling.  There is no evidence (so far) that this
     * was being used; however, png_set_background itself accepted and must still
     * accept '0' for the gamma value it takes, because it isn't always used.
     *
     * Since this is an API change (albeit a very minor one that removes an
     * undocumented API feature) the following checks were only enabled in
     * libpng-1.6.0.
     */
    if (file_gamma <= 0)
       png_error(png_ptr, "invalid file gamma in png_set_gamma");
    if (scrn_gamma <= 0)
       png_error(png_ptr, "invalid screen gamma in png_set_gamma");
    /* Set the gamma values unconditionally - this overrides the value in the PNG
     * file if a gAMA chunk was present.  png_set_alpha_mode provides a
     * different, easier, way to default the file gamma.
     */
    png_ptr->colorspace.gamma = file_gamma;
    png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
    png_ptr->screen_gamma = scrn_gamma;
 }
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
 {
    png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
       convert_gamma_value(png_ptr, file_gamma));
 }
 #  endif /* FLOATING_POINT_SUPPORTED */
 #endif /* READ_GAMMA */
 #ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expand paletted images to RGB, expand grayscale images of
  * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
  * to alpha channels.
  */
 void PNGAPI
 png_set_expand(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_expand");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 }
 /* GRR 19990627:  the following three functions currently are identical
  *  to png_set_expand().  However, it is entirely reasonable that someone
  *  might wish to expand an indexed image to RGB but *not* expand a single,
  *  fully transparent palette entry to a full alpha channel--perhaps instead
  *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
  *  the transparent color with a particular RGB value, or drop tRNS entirely.
  *  IOW, a future version of the library may make the transformations flag
  *  a bit more fine-grained, with separate bits for each of these three
  *  functions.
  *
  *  More to the point, these functions make it obvious what libpng will be
  *  doing, whereas "expand" can (and does) mean any number of things.
  *
  *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
  *  to expand only the sample depth but not to expand the tRNS to alpha
  *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
  */
 /* Expand paletted images to RGB. */
 void PNGAPI
 png_set_palette_to_rgb(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_palette_to_rgb");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 }
 /* Expand grayscale images of less than 8-bit depth to 8 bits. */
 void PNGAPI
 png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= PNG_EXPAND;
 }
 /* Expand tRNS chunks to alpha channels. */
 void PNGAPI
 png_set_tRNS_to_alpha(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_tRNS_to_alpha");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 }
 #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
 #ifdef PNG_READ_EXPAND_16_SUPPORTED
 /* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
  * it may not work correctly.)
  */
 void PNGAPI
 png_set_expand_16(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_expand_16");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
 }
 #endif
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 void PNGAPI
 png_set_gray_to_rgb(png_structrp png_ptr)
 {
    png_debug(1, "in png_set_gray_to_rgb");
    if (!png_rtran_ok(png_ptr, 0))
       return;
    /* Because rgb must be 8 bits or more: */
    png_set_expand_gray_1_2_4_to_8(png_ptr);
    png_ptr->transformations |= PNG_GRAY_TO_RGB;
 }
 #endif
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
 void PNGFAPI
 png_set_rgb_to_gray_fixed(png_structrp png_ptr, int error_action,
     png_fixed_point red, png_fixed_point green)
 {
    png_debug(1, "in png_set_rgb_to_gray");
    /* Need the IHDR here because of the check on color_type below. */
    /* TODO: fix this */
    if (!png_rtran_ok(png_ptr, 1))
       return;
    switch(error_action)
    {
       case PNG_ERROR_ACTION_NONE:
          png_ptr->transformations |= PNG_RGB_TO_GRAY;
          break;
       case PNG_ERROR_ACTION_WARN:
          png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
          break;
       case PNG_ERROR_ACTION_ERROR:
          png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
          break;
       default:
          png_error(png_ptr, "invalid error action to rgb_to_gray");
          break;
    }
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
 #ifdef PNG_READ_EXPAND_SUPPORTED
       png_ptr->transformations |= PNG_EXPAND;
 #else
    {
       /* Make this an error in 1.6 because otherwise the application may assume
        * that it just worked and get a memory overwrite.
        */
       png_error(png_ptr,
         "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");
       /* png_ptr->transformations &= ~PNG_RGB_TO_GRAY; */
    }
 #endif
    {
       if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
       {
          png_uint_16 red_int, green_int;
          /* NOTE: this calculation does not round, but this behavior is retained
           * for consistency, the inaccuracy is very small.  The code here always
           * overwrites the coefficients, regardless of whether they have been
           * defaulted or set already.
           */
          red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
          green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);
          png_ptr->rgb_to_gray_red_coeff   = red_int;
          png_ptr->rgb_to_gray_green_coeff = green_int;
          png_ptr->rgb_to_gray_coefficients_set = 1;
       }
       else
       {
          if (red >= 0 && green >= 0)
             png_app_warning(png_ptr,
                "ignoring out of range rgb_to_gray coefficients");
          /* Use the defaults, from the cHRM chunk if set, else the historical
           * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
           * png_do_rgb_to_gray for more discussion of the values.  In this case
           * the coefficients are not marked as 'set' and are not overwritten if
           * something has already provided a default.
           */
          if (png_ptr->rgb_to_gray_red_coeff == 0 &&
             png_ptr->rgb_to_gray_green_coeff == 0)
          {
             png_ptr->rgb_to_gray_red_coeff   = 6968;
             png_ptr->rgb_to_gray_green_coeff = 23434;
             /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
          }
       }
    }
 }
 #ifdef PNG_FLOATING_POINT_SUPPORTED
 /* Convert a RGB image to a grayscale of the same width.  This allows us,
  * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
  */
 void PNGAPI
 png_set_rgb_to_gray(png_structrp png_ptr, int error_action, double red,
    double green)
 {
    png_set_rgb_to_gray_fixed(png_ptr, error_action,
       png_fixed(png_ptr, red, "rgb to gray red coefficient"),
       png_fixed(png_ptr, green, "rgb to gray green coefficient"));
 }
 #endif /* FLOATING POINT */
 #endif /* RGB_TO_GRAY */
 #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
     defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
 void PNGAPI
 png_set_read_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
     read_user_transform_fn)
 {
    png_debug(1, "in png_set_read_user_transform_fn");
 #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    png_ptr->transformations |= PNG_USER_TRANSFORM;
    png_ptr->read_user_transform_fn = read_user_transform_fn;
 #endif
 }
 #endif
 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
 #ifdef PNG_READ_GAMMA_SUPPORTED
 /* In the case of gamma transformations only do transformations on images where
  * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
  * slows things down slightly, and also needlessly introduces small errors.
  */
 static int /* PRIVATE */
 png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
 {
    /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
     * correction as a difference of the overall transform from 1.0
     *
     * We want to compare the threshold with s*f - 1, if we get
     * overflow here it is because of wacky gamma values so we
     * turn on processing anyway.
     */
    png_fixed_point gtest;
    return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
        png_gamma_significant(gtest);
 }
 #endif
 /* Initialize everything needed for the read.  This includes modifying
  * the palette.
  */
 /*For the moment 'png_init_palette_transformations' and
  * 'png_init_rgb_transformations' only do some flag canceling optimizations.
  * The intent is that these two routines should have palette or rgb operations
  * extracted from 'png_init_read_transformations'.
  */
 static void /* PRIVATE */
 png_init_palette_transformations(png_structrp png_ptr)
 {
    /* Called to handle the (input) palette case.  In png_do_read_transformations
     * the first step is to expand the palette if requested, so this code must
     * take care to only make changes that are invariant with respect to the
     * palette expansion, or only do them if there is no expansion.
     *
     * STRIP_ALPHA has already been handled in the caller (by setting num_trans
     * to 0.)
     */
    int input_has_alpha = 0;
    int input_has_transparency = 0;
    if (png_ptr->num_trans > 0)
    {
       int i;
       /* Ignore if all the entries are opaque (unlikely!) */
       for (i=0; i<png_ptr->num_trans; ++i)
       {
          if (png_ptr->trans_alpha[i] == 255)
             continue;
          else if (png_ptr->trans_alpha[i] == 0)
             input_has_transparency = 1;
          else
          {
             input_has_transparency = 1;
             input_has_alpha = 1;
             break;
          }
       }
    }
    /* If no alpha we can optimize. */
    if (!input_has_alpha)
    {
       /* Any alpha means background and associative alpha processing is
        * required, however if the alpha is 0 or 1 throughout OPTIMIZE_ALPHA
        * and ENCODE_ALPHA are irrelevant.
        */
       png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
       if (!input_has_transparency)
          png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
    }
 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
    /* png_set_background handling - deals with the complexity of whether the
     * background color is in the file format or the screen format in the case
     * where an 'expand' will happen.
     */
    /* The following code cannot be entered in the alpha pre-multiplication case
     * because PNG_BACKGROUND_EXPAND is cancelled below.
     */
    if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
        (png_ptr->transformations & PNG_EXPAND))
    {
       {
          png_ptr->background.red   =
              png_ptr->palette[png_ptr->background.index].red;
          png_ptr->background.green =
              png_ptr->palette[png_ptr->background.index].green;
          png_ptr->background.blue  =
              png_ptr->palette[png_ptr->background.index].blue;
 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
         if (png_ptr->transformations & PNG_INVERT_ALPHA)
         {
            if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
            {
               /* Invert the alpha channel (in tRNS) unless the pixels are
                * going to be expanded, in which case leave it for later
                */
               int i, istop = png_ptr->num_trans;
               for (i=0; i<istop; i++)
                  png_ptr->trans_alpha[i] = (png_byte)(255 -
                     png_ptr->trans_alpha[i]);
            }
         }
 #endif /* PNG_READ_INVERT_ALPHA_SUPPORTED */
       }
    } /* background expand and (therefore) no alpha association. */
 #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
 }
 static void /* PRIVATE */
 png_init_rgb_transformations(png_structrp png_ptr)
 {
    /* Added to libpng-1.5.4: check the color type to determine whether there
     * is any alpha or transparency in the image and simply cancel the
     * background and alpha mode stuff if there isn't.
     */
    int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
    int input_has_transparency = png_ptr->num_trans > 0;
    /* If no alpha we can optimize. */
    if (!input_has_alpha)
    {
       /* Any alpha means background and associative alpha processing is
        * required, however if the alpha is 0 or 1 throughout OPTIMIZE_ALPHA
        * and ENCODE_ALPHA are irrelevant.
        */
 #     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
 #     endif
       if (!input_has_transparency)
          png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
    }
 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
    /* png_set_background handling - deals with the complexity of whether the
     * background color is in the file format or the screen format in the case
     * where an 'expand' will happen.
     */
    /* The following code cannot be entered in the alpha pre-multiplication case
     * because PNG_BACKGROUND_EXPAND is cancelled below.
     */
    if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
        (png_ptr->transformations & PNG_EXPAND) &&
        !(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
        /* i.e., GRAY or GRAY_ALPHA */
    {
       {
          /* Expand background and tRNS chunks */
          int gray = png_ptr->background.gray;
          int trans_gray = png_ptr->trans_color.gray;
          switch (png_ptr->bit_depth)
          {
             case 1:
                gray *= 0xff;
                trans_gray *= 0xff;
                break;
             case 2:
                gray *= 0x55;
                trans_gray *= 0x55;
                break;
             case 4:
                gray *= 0x11;
                trans_gray *= 0x11;
                break;
             default:
             case 8:
                /* FALL THROUGH (Already 8 bits) */
             case 16:
                /* Already a full 16 bits */
                break;
          }
          png_ptr->background.red = png_ptr->background.green =
             png_ptr->background.blue = (png_uint_16)gray;
          if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
          {
             png_ptr->trans_color.red = png_ptr->trans_color.green =
                png_ptr->trans_color.blue = (png_uint_16)trans_gray;
          }
       }
    } /* background expand and (therefore) no alpha association. */
 #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
 }
 void /* PRIVATE */
 png_init_read_transformations(png_structrp png_ptr)
 {
    png_debug(1, "in png_init_read_transformations");
    /* This internal function is called from png_read_start_row in pngrutil.c
     * and it is called before the 'rowbytes' calculation is done, so the code
     * in here can change or update the transformations flags.
     *
     * First do updates that do not depend on the details of the PNG image data
     * being processed.
     */
 #ifdef PNG_READ_GAMMA_SUPPORTED
    /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
     * png_set_alpha_mode and this is another source for a default file gamma so
     * the test needs to be performed later - here.  In addition prior to 1.5.4
     * the tests were repeated for the PALETTE color type here - this is no
     * longer necessary (and doesn't seem to have been necessary before.)
     */
    {
       /* The following temporary indicates if overall gamma correction is
        * required.
        */
       int gamma_correction = 0;
       if (png_ptr->colorspace.gamma != 0) /* has been set */
       {
          if (png_ptr->screen_gamma != 0) /* screen set too */
             gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
                png_ptr->screen_gamma);
          else
             /* Assume the output matches the input; a long time default behavior
              * of libpng, although the standard has nothing to say about this.
              */
             png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
       }
       else if (png_ptr->screen_gamma != 0)
          /* The converse - assume the file matches the screen, note that this
           * perhaps undesireable default can (from 1.5.4) be changed by calling
           * png_set_alpha_mode (even if the alpha handling mode isn't required
           * or isn't changed from the default.)
           */
          png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);
       else /* neither are set */
          /* Just in case the following prevents any processing - file and screen
           * are both assumed to be linear and there is no way to introduce a
           * third gamma value other than png_set_background with 'UNIQUE', and,
           * prior to 1.5.4
           */
          png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;
       /* We have a gamma value now. */
       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
       /* Now turn the gamma transformation on or off as appropriate.  Notice
        * that PNG_GAMMA just refers to the file->screen correction.  Alpha
        * composition may independently cause gamma correction because it needs
        * linear data (e.g. if the file has a gAMA chunk but the screen gamma
        * hasn't been specified.)  In any case this flag may get turned off in
        * the code immediately below if the transform can be handled outside the
        * row loop.
        */
       if (gamma_correction)
          png_ptr->transformations |= PNG_GAMMA;
       else
          png_ptr->transformations &= ~PNG_GAMMA;
    }
 #endif
    /* Certain transformations have the effect of preventing other
     * transformations that happen afterward in png_do_read_transformations,
     * resolve the interdependencies here.  From the code of
     * png_do_read_transformations the order is:
     *
     *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
     *  2) PNG_STRIP_ALPHA (if no compose)
     *  3) PNG_RGB_TO_GRAY
     *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
     *  5) PNG_COMPOSE
     *  6) PNG_GAMMA
     *  7) PNG_STRIP_ALPHA (if compose)
     *  8) PNG_ENCODE_ALPHA
     *  9) PNG_SCALE_16_TO_8
     * 10) PNG_16_TO_8
     * 11) PNG_QUANTIZE (converts to palette)
     * 12) PNG_EXPAND_16
     * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
     * 14) PNG_INVERT_MONO
     * 15) PNG_INVERT_ALPHA
     * 16) PNG_SHIFT
     * 17) PNG_PACK
     * 18) PNG_BGR
     * 19) PNG_PACKSWAP
     * 20) PNG_FILLER (includes PNG_ADD_ALPHA)
     * 21) PNG_SWAP_ALPHA
     * 22) PNG_SWAP_BYTES
     * 23) PNG_USER_TRANSFORM [must be last]
     */
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
       !(png_ptr->transformations & PNG_COMPOSE))
    {
       /* Stripping the alpha channel happens immediately after the 'expand'
        * transformations, before all other transformation, so it cancels out
        * the alpha handling.  It has the side effect negating the effect of
        * PNG_EXPAND_tRNS too:
        */
       png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
          PNG_EXPAND_tRNS);
       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
       /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
        * so transparency information would remain just so long as it wasn't
        * expanded.  This produces unexpected API changes if the set of things
        * that do PNG_EXPAND_tRNS changes (perfectly possible given the
        * documentation - which says ask for what you want, accept what you
        * get.)  This makes the behavior consistent from 1.5.4:
        */
       png_ptr->num_trans = 0;
    }
 #endif /* STRIP_ALPHA supported, no COMPOSE */
 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
    /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
     * settings will have no effect.
     */
    if (!png_gamma_significant(png_ptr->screen_gamma))
    {
       png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
    }
 #endif
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    /* Make sure the coefficients for the rgb to gray conversion are set
     * appropriately.
     */
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
       png_colorspace_set_rgb_coefficients(png_ptr);
 #endif
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
    /* Detect gray background and attempt to enable optimization for
     * gray --> RGB case.
     *
     * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
     * RGB_ALPHA (in which case need_expand is superfluous anyway), the
     * background color might actually be gray yet not be flagged as such.
     * This is not a problem for the current code, which uses
     * PNG_BACKGROUND_IS_GRAY only to decide when to do the
     * png_do_gray_to_rgb() transformation.
     *
     * TODO: this code needs to be revised to avoid the complexity and
     * interdependencies.  The color type of the background should be recorded in
     * png_set_background, along with the bit depth, then the code has a record
     * of exactly what color space the background is currently in.
     */
    if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
    {
       /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
        * the file was grayscale the background value is gray.
        */
       if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
          png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
    }
    else if (png_ptr->transformations & PNG_COMPOSE)
    {
       /* PNG_COMPOSE: png_set_background was called with need_expand false,
        * so the color is in the color space of the output or png_set_alpha_mode
        * was called and the color is black.  Ignore RGB_TO_GRAY because that
        * happens before GRAY_TO_RGB.
        */
       if (png_ptr->transformations & PNG_GRAY_TO_RGB)
       {
          if (png_ptr->background.red == png_ptr->background.green &&
              png_ptr->background.red == png_ptr->background.blue)
          {
             png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
             png_ptr->background.gray = png_ptr->background.red;
          }
       }
    }
 #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
 #endif /* PNG_READ_GRAY_TO_RGB_SUPPORTED */
    /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
     * can be performed directly on the palette, and some (such as rgb to gray)
     * can be optimized inside the palette.  This is particularly true of the
     * composite (background and alpha) stuff, which can be pretty much all done
     * in the palette even if the result is expanded to RGB or gray afterward.
     *
     * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
     * earlier and the palette stuff is actually handled on the first row.  This
     * leads to the reported bug that the palette returned by png_get_PLTE is not
     * updated.
     */
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       png_init_palette_transformations(png_ptr);
    else
       png_init_rgb_transformations(png_ptr);
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
    defined(PNG_READ_EXPAND_16_SUPPORTED)
    if ((png_ptr->transformations & PNG_EXPAND_16) &&
       (png_ptr->transformations & PNG_COMPOSE) &&
       !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
       png_ptr->bit_depth != 16)
    {
       /* TODO: fix this.  Because the expand_16 operation is after the compose
        * handling the background color must be 8, not 16, bits deep, but the
        * application will supply a 16-bit value so reduce it here.
        *
        * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
        * present, so that case is ok (until do_expand_16 is moved.)
        *
        * NOTE: this discards the low 16 bits of the user supplied background
        * color, but until expand_16 works properly there is no choice!
        */
 #     define CHOP(x) (x)=((png_uint_16)PNG_DIV257(x))
       CHOP(png_ptr->background.red);
       CHOP(png_ptr->background.green);
       CHOP(png_ptr->background.blue);
       CHOP(png_ptr->background.gray);
 #     undef CHOP
    }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
    (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
    defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
    if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
       (png_ptr->transformations & PNG_COMPOSE) &&
       !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
       png_ptr->bit_depth == 16)
    {
       /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
        * component this will also happen after PNG_COMPOSE and so the background
        * color must be pre-expanded here.
        *
        * TODO: fix this too.
        */
       png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
       png_ptr->background.green =
          (png_uint_16)(png_ptr->background.green * 257);
       png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
       png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
    }
 #endif
    /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
     * background support (see the comments in scripts/pnglibconf.dfa), this
     * allows pre-multiplication of the alpha channel to be implemented as
     * compositing on black.  This is probably sub-optimal and has been done in
     * 1.5.4 betas simply to enable external critique and testing (i.e. to
     * implement the new API quickly, without lots of internal changes.)
     */
 #ifdef PNG_READ_GAMMA_SUPPORTED
 #  ifdef PNG_READ_BACKGROUND_SUPPORTED
       /* Includes ALPHA_MODE */
       png_ptr->background_1 = png_ptr->background;
 #  endif
    /* This needs to change - in the palette image case a whole set of tables are
     * built when it would be quicker to just calculate the correct value for
     * each palette entry directly.  Also, the test is too tricky - why check
     * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
     * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
     * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
     * the gamma tables will not be built even if composition is required on a
     * gamma encoded value.
     *
     * In 1.5.4 this is addressed below by an additional check on the individual
     * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
     * tables.
     */
    if ((png_ptr->transformations & PNG_GAMMA)
       || ((png_ptr->transformations & PNG_RGB_TO_GRAY)
          && (png_gamma_significant(png_ptr->colorspace.gamma) ||
             png_gamma_significant(png_ptr->screen_gamma)))
       || ((png_ptr->transformations & PNG_COMPOSE)
          && (png_gamma_significant(png_ptr->colorspace.gamma)
             || png_gamma_significant(png_ptr->screen_gamma)
 #  ifdef PNG_READ_BACKGROUND_SUPPORTED
             || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE
                && png_gamma_significant(png_ptr->background_gamma))
 #  endif
       )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA)
          && png_gamma_significant(png_ptr->screen_gamma))
       )
    {
       png_build_gamma_table(png_ptr, png_ptr->bit_depth);
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
       if (png_ptr->transformations & PNG_COMPOSE)
       {
          /* Issue a warning about this combination: because RGB_TO_GRAY is
           * optimized to do the gamma transform if present yet do_background has
           * to do the same thing if both options are set a
           * double-gamma-correction happens.  This is true in all versions of
           * libpng to date.
           */
          if (png_ptr->transformations & PNG_RGB_TO_GRAY)
             png_warning(png_ptr,
                "libpng does not support gamma+background+rgb_to_gray");
          if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          {
             /* We don't get to here unless there is a tRNS chunk with non-opaque
              * entries - see the checking code at the start of this function.
              */
             png_color back, back_1;
             png_colorp palette = png_ptr->palette;
             int num_palette = png_ptr->num_palette;
             int i;
             if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
             {
                back.red = png_ptr->gamma_table[png_ptr->background.red];
                back.green = png_ptr->gamma_table[png_ptr->background.green];
                back.blue = png_ptr->gamma_table[png_ptr->background.blue];
                back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
                back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
                back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
             }
             else
             {
                png_fixed_point g, gs;
                switch (png_ptr->background_gamma_type)
                {
                   case PNG_BACKGROUND_GAMMA_SCREEN:
                      g = (png_ptr->screen_gamma);
                      gs = PNG_FP_1;
                      break;
                   case PNG_BACKGROUND_GAMMA_FILE:
                      g = png_reciprocal(png_ptr->colorspace.gamma);
                      gs = png_reciprocal2(png_ptr->colorspace.gamma,
                         png_ptr->screen_gamma);
                      break;
                   case PNG_BACKGROUND_GAMMA_UNIQUE:
                      g = png_reciprocal(png_ptr->background_gamma);
                      gs = png_reciprocal2(png_ptr->background_gamma,
                         png_ptr->screen_gamma);
                      break;
                   default:
                      g = PNG_FP_1;    /* back_1 */
                      gs = PNG_FP_1;   /* back */
                      break;
                }
                if (png_gamma_significant(gs))
                {
                   back.red = png_gamma_8bit_correct(png_ptr->background.red,
                       gs);
                   back.green = png_gamma_8bit_correct(png_ptr->background.green,
                       gs);
                   back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                       gs);
                }
                else
                {
                   back.red   = (png_byte)png_ptr->background.red;
                   back.green = (png_byte)png_ptr->background.green;
                   back.blue  = (png_byte)png_ptr->background.blue;
                }
                if (png_gamma_significant(g))
                {
                   back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
                      g);
                   back_1.green = png_gamma_8bit_correct(
                      png_ptr->background.green, g);
                   back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                      g);
                }
                else
                {
                   back_1.red   = (png_byte)png_ptr->background.red;
                   back_1.green = (png_byte)png_ptr->background.green;
                   back_1.blue  = (png_byte)png_ptr->background.blue;
                }
             }
             for (i = 0; i < num_palette; i++)
             {
                if (i < (int)png_ptr->num_trans &&
                    png_ptr->trans_alpha[i] != 0xff)
                {
                   if (png_ptr->trans_alpha[i] == 0)
                   {
                      palette[i] = back;
                   }
                   else /* if (png_ptr->trans_alpha[i] != 0xff) */
                   {
                      png_byte v, w;
                      v = png_ptr->gamma_to_1[palette[i].red];
                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
                      palette[i].red = png_ptr->gamma_from_1[w];
                      v = png_ptr->gamma_to_1[palette[i].green];
                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
                      palette[i].green = png_ptr->gamma_from_1[w];
                      v = png_ptr->gamma_to_1[palette[i].blue];
                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
                      palette[i].blue = png_ptr->gamma_from_1[w];
                   }
                }
                else
                {
                   palette[i].red = png_ptr->gamma_table[palette[i].red];
                   palette[i].green = png_ptr->gamma_table[palette[i].green];
                   palette[i].blue = png_ptr->gamma_table[palette[i].blue];
                }
             }
             /* Prevent the transformations being done again.
              *
              * NOTE: this is highly dubious; it removes the transformations in
              * place.  This seems inconsistent with the general treatment of the
              * transformations elsewhere.
              */
             png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
          } /* color_type == PNG_COLOR_TYPE_PALETTE */
          /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
          else /* color_type != PNG_COLOR_TYPE_PALETTE */
          {
             int gs_sig, g_sig;
             png_fixed_point g = PNG_FP_1;  /* Correction to linear */
             png_fixed_point gs = PNG_FP_1; /* Correction to screen */
             switch (png_ptr->background_gamma_type)
             {
                case PNG_BACKGROUND_GAMMA_SCREEN:
                   g = png_ptr->screen_gamma;
                   /* gs = PNG_FP_1; */
                   break;
                case PNG_BACKGROUND_GAMMA_FILE:
                   g = png_reciprocal(png_ptr->colorspace.gamma);
                   gs = png_reciprocal2(png_ptr->colorspace.gamma,
                      png_ptr->screen_gamma);
                   break;
                case PNG_BACKGROUND_GAMMA_UNIQUE:
                   g = png_reciprocal(png_ptr->background_gamma);
                   gs = png_reciprocal2(png_ptr->background_gamma,
                       png_ptr->screen_gamma);
                   break;
                default:
                   png_error(png_ptr, "invalid background gamma type");
             }
             g_sig = png_gamma_significant(g);
             gs_sig = png_gamma_significant(gs);
             if (g_sig)
                png_ptr->background_1.gray = png_gamma_correct(png_ptr,
                    png_ptr->background.gray, g);
             if (gs_sig)
                png_ptr->background.gray = png_gamma_correct(png_ptr,
                    png_ptr->background.gray, gs);
             if ((png_ptr->background.red != png_ptr->background.green) ||
                 (png_ptr->background.red != png_ptr->background.blue) ||
                 (png_ptr->background.red != png_ptr->background.gray))
             {
                /* RGB or RGBA with color background */
                if (g_sig)
                {
                   png_ptr->background_1.red = png_gamma_correct(png_ptr,
                       png_ptr->background.red, g);
                   png_ptr->background_1.green = png_gamma_correct(png_ptr,
                       png_ptr->background.green, g);
                   png_ptr->background_1.blue = png_gamma_correct(png_ptr,
                       png_ptr->background.blue, g);
                }
                if (gs_sig)
                {
                   png_ptr->background.red = png_gamma_correct(png_ptr,
                       png_ptr->background.red, gs);
                   png_ptr->background.green = png_gamma_correct(png_ptr,
                       png_ptr->background.green, gs);
                   png_ptr->background.blue = png_gamma_correct(png_ptr,
                       png_ptr->background.blue, gs);
                }
             }
             else
             {
                /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
                png_ptr->background_1.red = png_ptr->background_1.green
                    = png_ptr->background_1.blue = png_ptr->background_1.gray;
                png_ptr->background.red = png_ptr->background.green
                    = png_ptr->background.blue = png_ptr->background.gray;
             }
             /* The background is now in screen gamma: */
             png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
          } /* color_type != PNG_COLOR_TYPE_PALETTE */
       }/* png_ptr->transformations & PNG_BACKGROUND */
       else
       /* Transformation does not include PNG_BACKGROUND */
 #endif /* PNG_READ_BACKGROUND_SUPPORTED */
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
          /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
          && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
          (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
 #endif
          )
       {
          png_colorp palette = png_ptr->palette;
          int num_palette = png_ptr->num_palette;
          int i;
          /* NOTE: there are other transformations that should probably be in
           * here too.
           */
          for (i = 0; i < num_palette; i++)
          {
             palette[i].red = png_ptr->gamma_table[palette[i].red];
             palette[i].green = png_ptr->gamma_table[palette[i].green];
             palette[i].blue = png_ptr->gamma_table[palette[i].blue];
          }
          /* Done the gamma correction. */
          png_ptr->transformations &= ~PNG_GAMMA;
       } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
    }
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
    else
 #endif
 #endif /* PNG_READ_GAMMA_SUPPORTED */
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
    /* No GAMMA transformation (see the hanging else 4 lines above) */
    if ((png_ptr->transformations & PNG_COMPOSE) &&
        (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
    {
       int i;
       int istop = (int)png_ptr->num_trans;
       png_color back;
       png_colorp palette = png_ptr->palette;
       back.red   = (png_byte)png_ptr->background.red;
       back.green = (png_byte)png_ptr->background.green;
       back.blue  = (png_byte)png_ptr->background.blue;
       for (i = 0; i < istop; i++)
       {
          if (png_ptr->trans_alpha[i] == 0)
          {
             palette[i] = back;
          }
          else if (png_ptr->trans_alpha[i] != 0xff)
          {
             /* The png_composite() macro is defined in png.h */
             png_composite(palette[i].red, palette[i].red,
                 png_ptr->trans_alpha[i], back.red);
             png_composite(palette[i].green, palette[i].green,
                 png_ptr->trans_alpha[i], back.green);
             png_composite(palette[i].blue, palette[i].blue,
                 png_ptr->trans_alpha[i], back.blue);
          }
       }
       png_ptr->transformations &= ~PNG_COMPOSE;
    }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED */
 #ifdef PNG_READ_SHIFT_SUPPORTED
    if ((png_ptr->transformations & PNG_SHIFT) &&
       !(png_ptr->transformations & PNG_EXPAND) &&
        (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
    {
       int i;
       int istop = png_ptr->num_palette;
       int shift = 8 - png_ptr->sig_bit.red;
       png_ptr->transformations &= ~PNG_SHIFT;
       /* significant bits can be in the range 1 to 7 for a meaninful result, if
        * the number of significant bits is 0 then no shift is done (this is an
        * error condition which is silently ignored.)
        */
       if (shift > 0 && shift < 8)
          for (i=0; i<istop; ++i)
          {
             int component = png_ptr->palette[i].red;
             component >>= shift;
             png_ptr->palette[i].red = (png_byte)component;
          }
       shift = 8 - png_ptr->sig_bit.green;
       if (shift > 0 && shift < 8)
          for (i=0; i<istop; ++i)
          {
             int component = png_ptr->palette[i].green;
             component >>= shift;
             png_ptr->palette[i].green = (png_byte)component;
          }
       shift = 8 - png_ptr->sig_bit.blue;
       if (shift > 0 && shift < 8)
          for (i=0; i<istop; ++i)
          {
             int component = png_ptr->palette[i].blue;
             component >>= shift;
             png_ptr->palette[i].blue = (png_byte)component;
          }
    }
 #endif  /* PNG_READ_SHIFT_SUPPORTED */
 }
 /* Modify the info structure to reflect the transformations.  The
  * info should be updated so a PNG file could be written with it,
  * assuming the transformations result in valid PNG data.
  */
 void /* PRIVATE */
 png_read_transform_info(png_structrp png_ptr, png_inforp info_ptr)
 {
    png_debug(1, "in png_read_transform_info");
 #ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          /* This check must match what actually happens in
           * png_do_expand_palette; if it ever checks the tRNS chunk to see if
           * it is all opaque we must do the same (at present it does not.)
           */
          if (png_ptr->num_trans > 0)
             info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          else
             info_ptr->color_type = PNG_COLOR_TYPE_RGB;
          info_ptr->bit_depth = 8;
          info_ptr->num_trans = 0;
          if (png_ptr->palette == NULL)
             png_error (png_ptr, "Palette is NULL in indexed image");
       }
       else
       {
          if (png_ptr->num_trans)
          {
             if (png_ptr->transformations & PNG_EXPAND_tRNS)
                info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
          }
          if (info_ptr->bit_depth < 8)
             info_ptr->bit_depth = 8;
          info_ptr->num_trans = 0;
       }
    }
 #endif
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
    /* The following is almost certainly wrong unless the background value is in
     * the screen space!
     */
    if (png_ptr->transformations & PNG_COMPOSE)
       info_ptr->background = png_ptr->background;
 #endif
 #ifdef PNG_READ_GAMMA_SUPPORTED
    /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
     * however it seems that the code in png_init_read_transformations, which has
     * been called before this from png_read_update_info->png_read_start_row
     * sometimes does the gamma transform and cancels the flag.
     *
     * TODO: this looks wrong; the info_ptr should end up with a gamma equal to
     * the screen_gamma value.  The following probably results in weirdness if
     * the info_ptr is used by the app after the rows have been read.
     */
    info_ptr->colorspace.gamma = png_ptr->colorspace.gamma;
 #endif
    if (info_ptr->bit_depth == 16)
    {
 #  ifdef PNG_READ_16BIT_SUPPORTED
 #     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
          if (png_ptr->transformations & PNG_SCALE_16_TO_8)
             info_ptr->bit_depth = 8;
 #     endif
 #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
          if (png_ptr->transformations & PNG_16_TO_8)
             info_ptr->bit_depth = 8;
 #     endif
 #  else
       /* No 16 bit support: force chopping 16-bit input down to 8, in this case
        * the app program can chose if both APIs are available by setting the
        * correct scaling to use.
        */
 #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
          /* For compatibility with previous versions use the strip method by
           * default.  This code works because if PNG_SCALE_16_TO_8 is already
           * set the code below will do that in preference to the chop.
           */
          png_ptr->transformations |= PNG_16_TO_8;
          info_ptr->bit_depth = 8;
 #     else
 #        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
             png_ptr->transformations |= PNG_SCALE_16_TO_8;
             info_ptr->bit_depth = 8;
 #        else
             CONFIGURATION ERROR: you must enable at least one 16 to 8 method
 #        endif
 #    endif
 #endif /* !READ_16BIT_SUPPORTED */
    }
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    if (png_ptr->transformations & PNG_GRAY_TO_RGB)
       info_ptr->color_type = (png_byte)(info_ptr->color_type |
          PNG_COLOR_MASK_COLOR);
 #endif
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
       info_ptr->color_type = (png_byte)(info_ptr->color_type &
          ~PNG_COLOR_MASK_COLOR);
 #endif
 #ifdef PNG_READ_QUANTIZE_SUPPORTED
    if (png_ptr->transformations & PNG_QUANTIZE)
    {
       if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
           (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
           png_ptr->palette_lookup && info_ptr->bit_depth == 8)
       {
          info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
       }
    }
 #endif
 #ifdef PNG_READ_EXPAND_16_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
       info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
    {
       info_ptr->bit_depth = 16;
    }
 #endif
 #ifdef PNG_READ_PACK_SUPPORTED
    if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
       info_ptr->bit_depth = 8;
 #endif
    if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       info_ptr->channels = 1;
    else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
       info_ptr->channels = 3;
    else
       info_ptr->channels = 1;
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_STRIP_ALPHA)
    {
       info_ptr->color_type = (png_byte)(info_ptr->color_type &
          ~PNG_COLOR_MASK_ALPHA);
       info_ptr->num_trans = 0;
    }
 #endif
    if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
       info_ptr->channels++;
 #ifdef PNG_READ_FILLER_SUPPORTED
    /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
    if ((png_ptr->transformations & PNG_FILLER) &&
        ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
        (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
    {
       info_ptr->channels++;
       /* If adding a true alpha channel not just filler */
       if (png_ptr->transformations & PNG_ADD_ALPHA)
          info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
    }
 #endif
 #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
 defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
    {
       if (info_ptr->bit_depth < png_ptr->user_transform_depth)
          info_ptr->bit_depth = png_ptr->user_transform_depth;
       if (info_ptr->channels < png_ptr->user_transform_channels)
          info_ptr->channels = png_ptr->user_transform_channels;
    }
 #endif
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
        info_ptr->bit_depth);
    info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
    /* Adding in 1.5.4: cache the above value in png_struct so that we can later
     * check in png_rowbytes that the user buffer won't get overwritten.  Note
     * that the field is not always set - if png_read_update_info isn't called
     * the application has to either not do any transforms or get the calculation
     * right itself.
     */
    png_ptr->info_rowbytes = info_ptr->rowbytes;
 #ifndef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr)
       return;
 #endif
 }
 #ifdef PNG_READ_PACK_SUPPORTED
 /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
  * without changing the actual values.  Thus, if you had a row with
  * a bit depth of 1, you would end up with bytes that only contained
  * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
  * png_do_shift() after this.
  */
 static void
 png_do_unpack(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_unpack");
    if (row_info->bit_depth < 8)
    {
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;
       switch (row_info->bit_depth)
       {
          case 1:
          {
             png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
             png_bytep dp = row + (png_size_t)row_width - 1;
             png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x01);
                if (shift == 7)
                {
                   shift = 0;
                   sp--;
                }
                else
                   shift++;
                dp--;
             }
             break;
          }
          case 2:
          {
             png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
             png_bytep dp = row + (png_size_t)row_width - 1;
             png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x03);
                if (shift == 6)
                {
                   shift = 0;
                   sp--;
                }
                else
                   shift += 2;
                dp--;
             }
             break;
          }
          case 4:
          {
             png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
             png_bytep dp = row + (png_size_t)row_width - 1;
             png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x0f);
                if (shift == 4)
                {
                   shift = 0;
                   sp--;
                }
                else
                   shift = 4;
                dp--;
             }
             break;
          }
          default:
             break;
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_width * row_info->channels;
    }
 }
 #endif
 #ifdef PNG_READ_SHIFT_SUPPORTED
 /* Reverse the effects of png_do_shift.  This routine merely shifts the
  * pixels back to their significant bits values.  Thus, if you have
  * a row of bit depth 8, but only 5 are significant, this will shift
  * the values back to 0 through 31.
  */
 static void
 png_do_unshift(png_row_infop row_info, png_bytep row,
     png_const_color_8p sig_bits)
 {
    int color_type;
    png_debug(1, "in png_do_unshift");
    /* The palette case has already been handled in the _init routine. */
    color_type = row_info->color_type;
    if (color_type != PNG_COLOR_TYPE_PALETTE)
    {
       int shift[4];
       int channels = 0;
       int bit_depth = row_info->bit_depth;
       if (color_type & PNG_COLOR_MASK_COLOR)
       {
          shift[channels++] = bit_depth - sig_bits->red;
          shift[channels++] = bit_depth - sig_bits->green;
          shift[channels++] = bit_depth - sig_bits->blue;
       }
       else
       {
          shift[channels++] = bit_depth - sig_bits->gray;
       }
       if (color_type & PNG_COLOR_MASK_ALPHA)
       {
          shift[channels++] = bit_depth - sig_bits->alpha;
       }
       {
          int c, have_shift;
          for (c = have_shift = 0; c < channels; ++c)
          {
             /* A shift of more than the bit depth is an error condition but it
              * gets ignored here.
              */
             if (shift[c] <= 0 || shift[c] >= bit_depth)
                shift[c] = 0;
             else
                have_shift = 1;
          }
          if (!have_shift)
             return;
       }
       switch (bit_depth)
       {
          default:
          /* Must be 1bpp gray: should not be here! */
             /* NOTREACHED */
             break;
          case 2:
          /* Must be 2bpp gray */
          /* assert(channels == 1 && shift[0] == 1) */
          {
             png_bytep bp = row;
             png_bytep bp_end = bp + row_info->rowbytes;
             while (bp < bp_end)
             {
                int b = (*bp >> 1) & 0x55;
                *bp++ = (png_byte)b;
             }
             break;
          }
          case 4:
          /* Must be 4bpp gray */
          /* assert(channels == 1) */
          {
             png_bytep bp = row;
             png_bytep bp_end = bp + row_info->rowbytes;
             int gray_shift = shift[0];
             int mask =  0xf >> gray_shift;
             mask |= mask << 4;
             while (bp < bp_end)
             {
                int b = (*bp >> gray_shift) & mask;
                *bp++ = (png_byte)b;
             }
             break;
          }
          case 8:
          /* Single byte components, G, GA, RGB, RGBA */
          {
             png_bytep bp = row;
             png_bytep bp_end = bp + row_info->rowbytes;
             int channel = 0;
             while (bp < bp_end)
             {
                int b = *bp >> shift[channel];
                if (++channel >= channels)
                   channel = 0;
                *bp++ = (png_byte)b;
             }
             break;
          }
 #ifdef PNG_READ_16BIT_SUPPORTED
          case 16:
          /* Double byte components, G, GA, RGB, RGBA */
          {
             png_bytep bp = row;
             png_bytep bp_end = bp + row_info->rowbytes;
             int channel = 0;
             while (bp < bp_end)
             {
                int value = (bp[0] << 8) + bp[1];
                value >>= shift[channel];
                if (++channel >= channels)
                   channel = 0;
                *bp++ = (png_byte)(value >> 8);
                *bp++ = (png_byte)(value & 0xff);
             }
             break;
          }
 #endif
       }
    }
 }
 #endif
 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
 /* Scale rows of bit depth 16 down to 8 accurately */
 static void
 png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_scale_16_to_8");
    if (row_info->bit_depth == 16)
    {
       png_bytep sp = row; /* source */
       png_bytep dp = row; /* destination */
       png_bytep ep = sp + row_info->rowbytes; /* end+1 */
       while (sp < ep)
       {
          /* The input is an array of 16 bit components, these must be scaled to
           * 8 bits each.  For a 16 bit value V the required value (from the PNG
           * specification) is:
           *
           *    (V * 255) / 65535
           *
           * This reduces to round(V / 257), or floor((V + 128.5)/257)
           *
           * Represent V as the two byte value vhi.vlo.  Make a guess that the
           * result is the top byte of V, vhi, then the correction to this value
           * is:
           *
           *    error = floor(((V-vhi.vhi) + 128.5) / 257)
           *          = floor(((vlo-vhi) + 128.5) / 257)
           *
           * This can be approximated using integer arithmetic (and a signed
           * shift):
           *
           *    error = (vlo-vhi+128) >> 8;
           *
           * The approximate differs from the exact answer only when (vlo-vhi) is
           * 128; it then gives a correction of +1 when the exact correction is
           * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
           * input values) is:
           *
           *    error = (vlo-vhi+128)*65535 >> 24;
           *
           * An alternative arithmetic calculation which also gives no errors is:
           *
           *    (V * 255 + 32895) >> 16
           */
          png_int_32 tmp = *sp++; /* must be signed! */
          tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
          *dp++ = (png_byte)tmp;
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_info->width * row_info->channels;
    }
 }
 #endif
 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
 static void
 /* Simply discard the low byte.  This was the default behavior prior
  * to libpng-1.5.4.
  */
 png_do_chop(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_chop");
    if (row_info->bit_depth == 16)
    {
       png_bytep sp = row; /* source */
       png_bytep dp = row; /* destination */
       png_bytep ep = sp + row_info->rowbytes; /* end+1 */
       while (sp < ep)
       {
          *dp++ = *sp;
          sp += 2; /* skip low byte */
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_info->width * row_info->channels;
    }
 }
 #endif
 #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
 static void
 png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
 {
    png_debug(1, "in png_do_read_swap_alpha");
    {
       png_uint_32 row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
       {
          /* This converts from RGBA to ARGB */
          if (row_info->bit_depth == 8)
          {
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_byte save;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                save = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = save;
             }
          }
 #ifdef PNG_READ_16BIT_SUPPORTED
          /* This converts from RRGGBBAA to AARRGGBB */
          else
          {
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_byte save[2];
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                save[0] = *(--sp);
                save[1] = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = save[0];
                *(--dp) = save[1];
             }
          }
 #endif
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
          /* This converts from GA to AG */
          if (row_info->bit_depth == 8)
          {
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_byte save;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                save = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = save;
             }
          }
 #ifdef PNG_READ_16BIT_SUPPORTED
          /* This converts from GGAA to AAGG */
          else
          {
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_byte save[2];
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                save[0] = *(--sp);
                save[1] = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = save[0];
                *(--dp) = save[1];
             }
          }
 #endif
       }
    }
 }
 #endif
 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
 static void
 png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
 {
    png_uint_32 row_width;
    png_debug(1, "in png_do_read_invert_alpha");
    row_width = row_info->width;
    if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
    {
       if (row_info->bit_depth == 8)
       {
          /* This inverts the alpha channel in RGBA */
          png_bytep sp = row + row_info->rowbytes;
          png_bytep dp = sp;
          png_uint_32 i;
          for (i = 0; i < row_width; i++)
          {
             *(--dp) = (png_byte)(255 - *(--sp));
 /*          This does nothing:
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             We can replace it with:
 */
             sp-=3;
             dp=sp;
          }
       }
 #ifdef PNG_READ_16BIT_SUPPORTED
       /* This inverts the alpha channel in RRGGBBAA */
       else
       {
          png_bytep sp = row + row_info->rowbytes;
          png_bytep dp = sp;
          png_uint_32 i;
          for (i = 0; i < row_width; i++)
          {
             *(--dp) = (png_byte)(255 - *(--sp));
             *(--dp) = (png_byte)(255 - *(--sp));
 /*          This does nothing:
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
             We can replace it with:
 */
             sp-=6;
             dp=sp;
          }
       }
 #endif
    }
    else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
    {
       if (row_info->bit_depth == 8)
       {
          /* This inverts the alpha channel in GA */
          png_bytep sp = row + row_info->rowbytes;
          png_bytep dp = sp;
          png_uint_32 i;
          for (i = 0; i < row_width; i++)
          {
             *(--dp) = (png_byte)(255 - *(--sp));
             *(--dp) = *(--sp);
          }
       }
 #ifdef PNG_READ_16BIT_SUPPORTED
       else
       {
          /* This inverts the alpha channel in GGAA */
          png_bytep sp  = row + row_info->rowbytes;
          png_bytep dp = sp;
          png_uint_32 i;
          for (i = 0; i < row_width; i++)
          {
             *(--dp) = (png_byte)(255 - *(--sp));
             *(--dp) = (png_byte)(255 - *(--sp));
 /*
             *(--dp) = *(--sp);
             *(--dp) = *(--sp);
 */
             sp-=2;
             dp=sp;
          }
       }
 #endif
    }
 }
 #endif
 #ifdef PNG_READ_FILLER_SUPPORTED
 /* Add filler channel if we have RGB color */
 static void
 png_do_read_filler(png_row_infop row_info, png_bytep row,
     png_uint_32 filler, png_uint_32 flags)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
 #ifdef PNG_READ_16BIT_SUPPORTED
    png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
 #endif
    png_byte lo_filler = (png_byte)(filler & 0xff);
    png_debug(1, "in png_do_read_filler");
    if (
        row_info->color_type == PNG_COLOR_TYPE_GRAY)
    {
       if (row_info->bit_depth == 8)
       {
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
             /* This changes the data from G to GX */
             png_bytep sp = row + (png_size_t)row_width;
             png_bytep dp =  sp + (png_size_t)row_width;
             for (i = 1; i < row_width; i++)
             {
                *(--dp) = lo_filler;
                *(--dp) = *(--sp);
             }
             *(--dp) = lo_filler;
             row_info->channels = 2;
             row_info->pixel_depth = 16;
             row_info->rowbytes = row_width * 2;
          }
          else
          {
             /* This changes the data from G to XG */
             png_bytep sp = row + (png_size_t)row_width;
             png_bytep dp = sp  + (png_size_t)row_width;
             for (i = 0; i < row_width; i++)
             {
                *(--dp) = *(--sp);
                *(--dp) = lo_filler;
             }
             row_info->channels = 2;
             row_info->pixel_depth = 16;
             row_info->rowbytes = row_width * 2;
          }
       }
 #ifdef PNG_READ_16BIT_SUPPORTED
       else if (row_info->bit_depth == 16)
       {
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
             /* This changes the data from GG to GGXX */
             png_bytep sp = row + (png_size_t)row_width * 2;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 1; i < row_width; i++)
             {
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
             }
             *(--dp) = hi_filler;
             *(--dp) = lo_filler;
             row_info->channels = 2;
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
          else
          {
             /* This changes the data from GG to XXGG */
             png_bytep sp = row + (png_size_t)row_width * 2;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
             {
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
             }
             row_info->channels = 2;
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
       }
 #endif
    } /* COLOR_TYPE == GRAY */
    else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
    {
       if (row_info->bit_depth == 8)
       {
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
             /* This changes the data from RGB to RGBX */
             png_bytep sp = row + (png_size_t)row_width * 3;
             png_bytep dp = sp  + (png_size_t)row_width;
             for (i = 1; i < row_width; i++)
             {
                *(--dp) = lo_filler;
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
             }
             *(--dp) = lo_filler;
             row_info->channels = 4;
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
          else
          {
             /* This changes the data from RGB to XRGB */
             png_bytep sp = row + (png_size_t)row_width * 3;
             png_bytep dp = sp + (png_size_t)row_width;
             for (i = 0; i < row_width; i++)
             {
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = lo_filler;
             }
             row_info->channels = 4;
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
       }
 #ifdef PNG_READ_16BIT_SUPPORTED
       else if (row_info->bit_depth == 16)
       {
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
             /* This changes the data from RRGGBB to RRGGBBXX */
             png_bytep sp = row + (png_size_t)row_width * 6;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 1; i < row_width; i++)
             {
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
             }
             *(--dp) = hi_filler;
             *(--dp) = lo_filler;
             row_info->channels = 4;
             row_info->pixel_depth = 64;
             row_info->rowbytes = row_width * 8;
          }
          else
          {
             /* This changes the data from RRGGBB to XXRRGGBB */
             png_bytep sp = row + (png_size_t)row_width * 6;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
             {
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
             }
             row_info->channels = 4;
             row_info->pixel_depth = 64;
             row_info->rowbytes = row_width * 8;
          }
       }
 #endif
    } /* COLOR_TYPE == RGB */
 }
 #endif
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 /* Expand grayscale files to RGB, with or without alpha */
 static void
 png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
    png_debug(1, "in png_do_gray_to_rgb");
    if (row_info->bit_depth >= 8 &&
        !(row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          if (row_info->bit_depth == 8)
          {
             /* This changes G to RGB */
             png_bytep sp = row + (png_size_t)row_width - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
             {
                *(dp--) = *sp;
                *(dp--) = *sp;
                *(dp--) = *(sp--);
             }
          }
          else
          {
             /* This changes GG to RRGGBB */
             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 4;
             for (i = 0; i < row_width; i++)
             {
                *(dp--) = *sp;
                *(dp--) = *(sp - 1);
                *(dp--) = *sp;
                *(dp--) = *(sp - 1);
                *(dp--) = *(sp--);
                *(dp--) = *(sp--);
             }
          }
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
          if (row_info->bit_depth == 8)
          {
             /* This changes GA to RGBA */
             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
             {
                *(dp--) = *(sp--);
                *(dp--) = *sp;
                *(dp--) = *sp;
                *(dp--) = *(sp--);
             }
          }
          else
          {
             /* This changes GGAA to RRGGBBAA */
             png_bytep sp = row + (png_size_t)row_width * 4 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 4;
             for (i = 0; i < row_width; i++)
             {
                *(dp--) = *(sp--);
                *(dp--) = *(sp--);
                *(dp--) = *sp;
                *(dp--) = *(sp - 1);
                *(dp--) = *sp;
                *(dp--) = *(sp - 1);
                *(dp--) = *(sp--);
                *(dp--) = *(sp--);
             }
          }
       }
       row_info->channels = (png_byte)(row_info->channels + 2);
       row_info->color_type |= PNG_COLOR_MASK_COLOR;
       row_info->pixel_depth = (png_byte)(row_info->channels *
           row_info->bit_depth);
       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
    }
 }
 #endif
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
 /* Reduce RGB files to grayscale, with or without alpha
  * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
  * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
  * versions dated 1998 through November 2002 have been archived at
  * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
  * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
  * Charles Poynton poynton at poynton.com
  *
  *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
  *
  *  which can be expressed with integers as
  *
  *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
  *
  * Poynton's current link (as of January 2003 through July 2011):
  * <http://www.poynton.com/notes/colour_and_gamma/>
  * has changed the numbers slightly:
  *
  *     Y = 0.2126*R + 0.7152*G + 0.0722*B
  *
  *  which can be expressed with integers as
  *
  *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
  *
  *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
  *  end point chromaticities and the D65 white point.  Depending on the
  *  precision used for the D65 white point this produces a variety of different
  *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
  *  used (0.3127,0.3290) the Y calculation would be:
  *
  *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
  *
  *  While this is correct the rounding results in an overflow for white, because
  *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
  *  libpng uses, instead, the closest non-overflowing approximation:
  *
  *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
  *
  *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
  *  (including an sRGB chunk) then the chromaticities are used to calculate the
  *  coefficients.  See the chunk handling in pngrutil.c for more information.
  *
  *  In all cases the calculation is to be done in a linear colorspace.  If no
  *  gamma information is available to correct the encoding of the original RGB
  *  values this results in an implicit assumption that the original PNG RGB
  *  values were linear.
  *
  *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
  *  the API takes just red and green coefficients the blue coefficient is
  *  calculated to make the sum 32768.  This will result in different rounding
  *  to that used above.
  */
 static int
 png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
 {
    int rgb_error = 0;
    png_debug(1, "in png_do_rgb_to_gray");
    if (!(row_info->color_type & PNG_COLOR_MASK_PALETTE) &&
        (row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
       PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
       PNG_CONST png_uint_32 bc = 32768 - rc - gc;
       PNG_CONST png_uint_32 row_width = row_info->width;
       PNG_CONST int have_alpha =
          (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
       if (row_info->bit_depth == 8)
       {
 #ifdef PNG_READ_GAMMA_SUPPORTED
          /* Notice that gamma to/from 1 are not necessarily inverses (if
           * there is an overall gamma correction).  Prior to 1.5.5 this code
           * checked the linearized values for equality; this doesn't match
           * the documentation, the original values must be checked.
           */
          if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
          {
             png_bytep sp = row;
             png_bytep dp = row;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                png_byte red   = *(sp++);
                png_byte green = *(sp++);
                png_byte blue  = *(sp++);
                if (red != green || red != blue)
                {
                   red = png_ptr->gamma_to_1[red];
                   green = png_ptr->gamma_to_1[green];
                   blue = png_ptr->gamma_to_1[blue];
                   rgb_error |= 1;
                   *(dp++) = png_ptr->gamma_from_1[
                       (rc*red + gc*green + bc*blue + 16384)>>15];
                }
                else
                {
                   /* If there is no overall correction the table will not be
                    * set.
                    */
                   if (png_ptr->gamma_table != NULL)
                      red = png_ptr->gamma_table[red];
                   *(dp++) = red;
                }
                if (have_alpha)
                   *(dp++) = *(sp++);
             }
          }
          else
 #endif
          {
             png_bytep sp = row;
             png_bytep dp = row;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                png_byte red   = *(sp++);
                png_byte green = *(sp++);
                png_byte blue  = *(sp++);
                if (red != green || red != blue)
                {
                   rgb_error |= 1;
                   /* NOTE: this is the historical approach which simply
                    * truncates the results.
                    */
                   *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
                }
                else
                   *(dp++) = red;
                if (have_alpha)
                   *(dp++) = *(sp++);
             }
          }
       }
       else /* RGB bit_depth == 16 */
       {
 #ifdef PNG_READ_GAMMA_SUPPORTED
          if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
          {
             png_bytep sp = row;
             png_bytep dp = row;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                png_uint_16 red, green, blue, w;
                red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                if (red == green && red == blue)
                {
                   if (png_ptr->gamma_16_table != NULL)
                      w = png_ptr->gamma_16_table[(red&0xff)
                          >> png_ptr->gamma_shift][red>>8];
                   else
                      w = red;
                }
                else
                {
                   png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
                       >> png_ptr->gamma_shift][red>>8];
                   png_uint_16 green_1 =
                       png_ptr->gamma_16_to_1[(green&0xff) >>
                       png_ptr->gamma_shift][green>>8];
                   png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
                       >> png_ptr->gamma_shift][blue>>8];
                   png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
                       + bc*blue_1 + 16384)>>15);
                   w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
                       png_ptr->gamma_shift][gray16 >> 8];
                   rgb_error |= 1;
                }
                *(dp++) = (png_byte)((w>>8) & 0xff);
                *(dp++) = (png_byte)(w & 0xff);
                if (have_alpha)
                {
                   *(dp++) = *(sp++);
                   *(dp++) = *(sp++);
                }
             }
          }
          else
 #endif
          {
             png_bytep sp = row;
             png_bytep dp = row;
             png_uint_32 i;
             for (i = 0; i < row_width; i++)
             {
                png_uint_16 red, green, blue, gray16;
                red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                if (red != green || red != blue)
                   rgb_error |= 1;
                /* From 1.5.5 in the 16 bit case do the accurate conversion even
                 * in the 'fast' case - this is because this is where the code
                 * ends up when handling linear 16 bit data.
                 */
                gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
 );
                *(dp++) = (png_byte)((gray16>>8) & 0xff);
                *(dp++) = (png_byte)(gray16 & 0xff);
                if (have_alpha)
                {
                   *(dp++) = *(sp++);
                   *(dp++) = *(sp++);
                }
             }
          }
       }
       row_info->channels = (png_byte)(row_info->channels - 2);
       row_info->color_type = (png_byte)(row_info->color_type &
           ~PNG_COLOR_MASK_COLOR);
       row_info->pixel_depth = (png_byte)(row_info->channels *
           row_info->bit_depth);
       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
    }
    return rgb_error;
 }
 #endif
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
 /* Replace any alpha or transparency with the supplied background color.
  * "background" is already in the screen gamma, while "background_1" is
  * at a gamma of 1.0.  Paletted files have already been taken care of.
  */
 static void
 png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
 {
 #ifdef PNG_READ_GAMMA_SUPPORTED
    png_const_bytep gamma_table = png_ptr->gamma_table;
    png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
    png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
    png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
    png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
    png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
    int gamma_shift = png_ptr->gamma_shift;
    int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
 #endif
    png_bytep sp;
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
    int shift;
    png_debug(1, "in png_do_compose");
    {
       switch (row_info->color_type)
       {
          case PNG_COLOR_TYPE_GRAY:
          {
             switch (row_info->bit_depth)
             {
                case 1:
                {
                   sp = row;
                   shift = 7;
                   for (i = 0; i < row_width; i++)
                   {
                      if ((png_uint_16)((*sp >> shift) & 0x01)
                         == png_ptr->trans_color.gray)
                      {
                         unsigned int tmp = *sp & (0x7f7f >> (7 - shift));
                         tmp |= png_ptr->background.gray << shift;
                         *sp = (png_byte)(tmp & 0xff);
                      }
                      if (!shift)
                      {
                         shift = 7;
                         sp++;
                      }
                      else
                         shift--;
                   }
                   break;
                }
                case 2:
                {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      shift = 6;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x03)
                             == png_ptr->trans_color.gray)
                         {
                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                            tmp |= png_ptr->background.gray << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         else
                         {
                            unsigned int p = (*sp >> shift) & 0x03;
                            unsigned int g = (gamma_table [p | (p << 2) |
                                (p << 4) | (p << 6)] >> 6) & 0x03;
                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                            tmp |= g << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         if (!shift)
                         {
                            shift = 6;
                            sp++;
                         }
                         else
                            shift -= 2;
                      }
                   }
                   else
 #endif
                   {
                      sp = row;
                      shift = 6;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x03)
                             == png_ptr->trans_color.gray)
                         {
                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                            tmp |= png_ptr->background.gray << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         if (!shift)
                         {
                            shift = 6;
                            sp++;
                         }
                         else
                            shift -= 2;
                      }
                   }
                   break;
                }
                case 4:
                {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      shift = 4;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x0f)
                             == png_ptr->trans_color.gray)
                         {
                            unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                            tmp |= png_ptr->background.gray << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         else
                         {
                            unsigned int p = (*sp >> shift) & 0x0f;
                            unsigned int g = (gamma_table[p | (p << 4)] >> 4) &
 x0f;
                            unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                            tmp |= g << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         if (!shift)
                         {
                            shift = 4;
                            sp++;
                         }
                         else
                            shift -= 4;
                      }
                   }
                   else
 #endif
                   {
                      sp = row;
                      shift = 4;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x0f)
                             == png_ptr->trans_color.gray)
                         {
                            unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                            tmp |= png_ptr->background.gray << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }
                         if (!shift)
                         {
                            shift = 4;
                            sp++;
                         }
                         else
                            shift -= 4;
                      }
                   }
                   break;
                }
                case 8:
                {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp++)
                      {
                         if (*sp == png_ptr->trans_color.gray)
                            *sp = (png_byte)png_ptr->background.gray;
                         else
                            *sp = gamma_table[*sp];
                      }
                   }
                   else
 #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp++)
                      {
                         if (*sp == png_ptr->trans_color.gray)
                            *sp = (png_byte)png_ptr->background.gray;
                      }
                   }
                   break;
                }
                case 16:
                {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 2)
                      {
                         png_uint_16 v;
                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         if (v == png_ptr->trans_color.gray)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)((png_ptr->background.gray >> 8)
                                 & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.gray
                                 & 0xff);
                         }
                         else
                         {
                            v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);
                         }
                      }
                   }
                   else
 #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 2)
                      {
                         png_uint_16 v;
                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         if (v == png_ptr->trans_color.gray)
                         {
                            *sp = (png_byte)((png_ptr->background.gray >> 8)
                                 & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.gray
                                 & 0xff);
                         }
                      }
                   }
                   break;
                }
                default:
                   break;
             }
             break;
          }
          case PNG_COLOR_TYPE_RGB:
          {
             if (row_info->bit_depth == 8)
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_table != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 3)
                   {
                      if (*sp == png_ptr->trans_color.red &&
                          *(sp + 1) == png_ptr->trans_color.green &&
                          *(sp + 2) == png_ptr->trans_color.blue)
                      {
                         *sp = (png_byte)png_ptr->background.red;
                         *(sp + 1) = (png_byte)png_ptr->background.green;
                         *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
                      else
                      {
                         *sp = gamma_table[*sp];
                         *(sp + 1) = gamma_table[*(sp + 1)];
                         *(sp + 2) = gamma_table[*(sp + 2)];
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 3)
                   {
                      if (*sp == png_ptr->trans_color.red &&
                          *(sp + 1) == png_ptr->trans_color.green &&
                          *(sp + 2) == png_ptr->trans_color.blue)
                      {
                         *sp = (png_byte)png_ptr->background.red;
                         *(sp + 1) = (png_byte)png_ptr->background.green;
                         *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 6)
                   {
                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                      png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                          + *(sp + 3));
                      png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                          + *(sp + 5));
                      if (r == png_ptr->trans_color.red &&
                          g == png_ptr->trans_color.green &&
                          b == png_ptr->trans_color.blue)
                      {
                         /* Background is already in screen gamma */
                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                 & 0xff);
                         *(sp + 3) = (png_byte)(png_ptr->background.green
                                 & 0xff);
                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                 & 0xff);
                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
                      else
                      {
                         png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 3) = (png_byte)(v & 0xff);
                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 5) = (png_byte)(v & 0xff);
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 6)
                   {
                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                      png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                          + *(sp + 3));
                      png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                          + *(sp + 5));
                      if (r == png_ptr->trans_color.red &&
                          g == png_ptr->trans_color.green &&
                          b == png_ptr->trans_color.blue)
                      {
                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                 & 0xff);
                         *(sp + 3) = (png_byte)(png_ptr->background.green
                                 & 0xff);
                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                 & 0xff);
                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
                   }
                }
             }
             break;
          }
          case PNG_COLOR_TYPE_GRAY_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 2)
                   {
                      png_uint_16 a = *(sp + 1);
                      if (a == 0xff)
                         *sp = gamma_table[*sp];
                      else if (a == 0)
                      {
                         /* Background is already in screen gamma */
                         *sp = (png_byte)png_ptr->background.gray;
                      }
                      else
                      {
                         png_byte v, w;
                         v = gamma_to_1[*sp];
                         png_composite(w, v, a, png_ptr->background_1.gray);
                         if (!optimize)
                            w = gamma_from_1[w];
                         *sp = w;
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 2)
                   {
                      png_byte a = *(sp + 1);
                      if (a == 0)
                         *sp = (png_byte)png_ptr->background.gray;
                      else if (a < 0xff)
                         png_composite(*sp, *sp, a, png_ptr->background.gray);
                   }
                }
             }
             else /* if (png_ptr->bit_depth == 16) */
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                          + *(sp + 3));
                      if (a == (png_uint_16)0xffff)
                      {
                         png_uint_16 v;
                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
                      }
                      else if (a == 0)
                      {
                         /* Background is already in screen gamma */
                         *sp = (png_byte)((png_ptr->background.gray >> 8)
                                 & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                      }
                      else
                      {
                         png_uint_16 g, v, w;
                         g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                         png_composite_16(v, g, a, png_ptr->background_1.gray);
                         if (optimize)
                            w = v;
                         else
                            w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
                         *sp = (png_byte)((w >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(w & 0xff);
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                          + *(sp + 3));
                      if (a == 0)
                      {
                         *sp = (png_byte)((png_ptr->background.gray >> 8)
                                 & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                      }
                      else if (a < 0xffff)
                      {
                         png_uint_16 g, v;
                         g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         png_composite_16(v, g, a, png_ptr->background.gray);
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
                      }
                   }
                }
             }
             break;
          }
          case PNG_COLOR_TYPE_RGB_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_byte a = *(sp + 3);
                      if (a == 0xff)
                      {
                         *sp = gamma_table[*sp];
                         *(sp + 1) = gamma_table[*(sp + 1)];
                         *(sp + 2) = gamma_table[*(sp + 2)];
                      }
                      else if (a == 0)
                      {
                         /* Background is already in screen gamma */
                         *sp = (png_byte)png_ptr->background.red;
                         *(sp + 1) = (png_byte)png_ptr->background.green;
                         *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
                      else
                      {
                         png_byte v, w;
                         v = gamma_to_1[*sp];
                         png_composite(w, v, a, png_ptr->background_1.red);
                         if (!optimize) w = gamma_from_1[w];
                         *sp = w;
                         v = gamma_to_1[*(sp + 1)];
                         png_composite(w, v, a, png_ptr->background_1.green);
                         if (!optimize) w = gamma_from_1[w];
                         *(sp + 1) = w;
                         v = gamma_to_1[*(sp + 2)];
                         png_composite(w, v, a, png_ptr->background_1.blue);
                         if (!optimize) w = gamma_from_1[w];
                         *(sp + 2) = w;
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_byte a = *(sp + 3);
                      if (a == 0)
                      {
                         *sp = (png_byte)png_ptr->background.red;
                         *(sp + 1) = (png_byte)png_ptr->background.green;
                         *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
                      else if (a < 0xff)
                      {
                         png_composite(*sp, *sp, a, png_ptr->background.red);
                         png_composite(*(sp + 1), *(sp + 1), a,
                             png_ptr->background.green);
                         png_composite(*(sp + 2), *(sp + 2), a,
                             png_ptr->background.blue);
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
 #ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 8)
                   {
                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                          << 8) + (png_uint_16)(*(sp + 7)));
                      if (a == (png_uint_16)0xffff)
                      {
                         png_uint_16 v;
                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 3) = (png_byte)(v & 0xff);
                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 5) = (png_byte)(v & 0xff);
                      }
                      else if (a == 0)
                      {
                         /* Background is already in screen gamma */
                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                 & 0xff);
                         *(sp + 3) = (png_byte)(png_ptr->background.green
                                 & 0xff);
                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                 & 0xff);
                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
                      else
                      {
                         png_uint_16 v, w;
                         v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                         png_composite_16(w, v, a, png_ptr->background_1.red);
                         if (!optimize)
                            w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
 ];
                         *sp = (png_byte)((w >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(w & 0xff);
                         v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
                         png_composite_16(w, v, a, png_ptr->background_1.green);
                         if (!optimize)
                            w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
 ];
                         *(sp + 2) = (png_byte)((w >> 8) & 0xff);
                         *(sp + 3) = (png_byte)(w & 0xff);
                         v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
                         png_composite_16(w, v, a, png_ptr->background_1.blue);
                         if (!optimize)
                            w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
 ];
                         *(sp + 4) = (png_byte)((w >> 8) & 0xff);
                         *(sp + 5) = (png_byte)(w & 0xff);
                      }
                   }
                }
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 8)
                   {
                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                          << 8) + (png_uint_16)(*(sp + 7)));
                      if (a == 0)
                      {
                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                 & 0xff);
                         *(sp + 3) = (png_byte)(png_ptr->background.green
                                 & 0xff);
                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                 & 0xff);
                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
                      else if (a < 0xffff)
                      {
                         png_uint_16 v;
                         png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                         png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                             + *(sp + 3));
                         png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                             + *(sp + 5));
                         png_composite_16(v, r, a, png_ptr->background.red);
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
                         png_composite_16(v, g, a, png_ptr->background.green);
                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 3) = (png_byte)(v & 0xff);
                         png_composite_16(v, b, a, png_ptr->background.blue);
                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 5) = (png_byte)(v & 0xff);
                      }
                   }
                }
             }
             break;
          }
          default:
             break;
       }
    }
 }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */
 #ifdef PNG_READ_GAMMA_SUPPORTED
 /* Gamma correct the image, avoiding the alpha channel.  Make sure
  * you do this after you deal with the transparency issue on grayscale
  * or RGB images. If your bit depth is 8, use gamma_table, if it
  * is 16, use gamma_16_table and gamma_shift.  Build these with
  * build_gamma_table().
  */
 static void
 png_do_gamma(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
 {
    png_const_bytep gamma_table = png_ptr->gamma_table;
    png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
    int gamma_shift = png_ptr->gamma_shift;
    png_bytep sp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
    png_debug(1, "in png_do_gamma");
    if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
        (row_info->bit_depth == 16 && gamma_16_table != NULL)))
    {
       switch (row_info->color_type)
       {
          case PNG_COLOR_TYPE_RGB:
          {
             if (row_info->bit_depth == 8)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   *sp = gamma_table[*sp];
                   sp++;
                   *sp = gamma_table[*sp];
                   sp++;
                   *sp = gamma_table[*sp];
                   sp++;
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 v;
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                }
             }
             break;
          }
          case PNG_COLOR_TYPE_RGB_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   *sp = gamma_table[*sp];
                   sp++;
                   *sp = gamma_table[*sp];
                   sp++;
                   *sp = gamma_table[*sp];
                   sp++;
                   sp++;
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 4;
                }
             }
             break;
          }
          case PNG_COLOR_TYPE_GRAY_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   *sp = gamma_table[*sp];
                   sp += 2;
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 4;
                }
             }
             break;
          }
          case PNG_COLOR_TYPE_GRAY:
          {
             if (row_info->bit_depth == 2)
             {
                sp = row;
                for (i = 0; i < row_width; i += 4)
                {
                   int a = *sp & 0xc0;
                   int b = *sp & 0x30;
                   int c = *sp & 0x0c;
                   int d = *sp & 0x03;
                   *sp = (png_byte)(
                       ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
                       ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
                       ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
                       ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
                   sp++;
                }
             }
             if (row_info->bit_depth == 4)
             {
                sp = row;
                for (i = 0; i < row_width; i += 2)
                {
                   int msb = *sp & 0xf0;
                   int lsb = *sp & 0x0f;
                   *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
                       | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
                   sp++;
                }
             }
             else if (row_info->bit_depth == 8)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   *sp = gamma_table[*sp];
                   sp++;
                }
             }
             else if (row_info->bit_depth == 16)
             {
                sp = row;
                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
                }
             }
             break;
          }
          default:
             break;
       }
    }
 }
 #endif
 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
 /* Encode the alpha channel to the output gamma (the input channel is always
  * linear.)  Called only with color types that have an alpha channel.  Needs the
  * from_1 tables.
  */
 static void
 png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
 {
    png_uint_32 row_width = row_info->width;
    png_debug(1, "in png_do_encode_alpha");
    if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
    {
       if (row_info->bit_depth == 8)
       {
          PNG_CONST png_bytep table = png_ptr->gamma_from_1;
          if (table != NULL)
          {
             PNG_CONST int step =
                (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
             /* The alpha channel is the last component: */
             row += step - 1;
             for (; row_width > 0; --row_width, row += step)
                *row = table[*row];
             return;
          }
       }
       else if (row_info->bit_depth == 16)
       {
          PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
          PNG_CONST int gamma_shift = png_ptr->gamma_shift;
          if (table != NULL)
          {
             PNG_CONST int step =
                (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
             /* The alpha channel is the last component: */
             row += step - 2;
             for (; row_width > 0; --row_width, row += step)
             {
                png_uint_16 v;
                v = table[*(row + 1) >> gamma_shift][*row];
                *row = (png_byte)((v >> 8) & 0xff);
                *(row + 1) = (png_byte)(v & 0xff);
             }
             return;
          }
       }
    }
    /* Only get to here if called with a weird row_info; no harm has been done,
     * so just issue a warning.
     */
    png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
 }
 #endif
 #ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expands a palette row to an RGB or RGBA row depending
  * upon whether you supply trans and num_trans.
  */
 static void
 png_do_expand_palette(png_row_infop row_info, png_bytep row,
    png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
    png_debug(1, "in png_do_expand_palette");
    if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
    {
       if (row_info->bit_depth < 8)
       {
          switch (row_info->bit_depth)
          {
             case 1:
             {
                sp = row + (png_size_t)((row_width - 1) >> 3);
                dp = row + (png_size_t)row_width - 1;
                shift = 7 - (int)((row_width + 7) & 0x07);
                for (i = 0; i < row_width; i++)
                {
                   if ((*sp >> shift) & 0x01)
                      *dp = 1;
                   else
                      *dp = 0;
                   if (shift == 7)
                   {
                      shift = 0;
                      sp--;
                   }
                   else
                      shift++;
                   dp--;
                }
                break;
             }
             case 2:
             {
                sp = row + (png_size_t)((row_width - 1) >> 2);
                dp = row + (png_size_t)row_width - 1;
                shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                for (i = 0; i < row_width; i++)
                {
                   value = (*sp >> shift) & 0x03;
                   *dp = (png_byte)value;
                   if (shift == 6)
                   {
                      shift = 0;
                      sp--;
                   }
                   else
                      shift += 2;
                   dp--;
                }
                break;
             }
             case 4:
             {
                sp = row + (png_size_t)((row_width - 1) >> 1);
                dp = row + (png_size_t)row_width - 1;
                shift = (int)((row_width & 0x01) << 2);
                for (i = 0; i < row_width; i++)
                {
                   value = (*sp >> shift) & 0x0f;
                   *dp = (png_byte)value;
                   if (shift == 4)
                   {
                      shift = 0;
                      sp--;
                   }
                   else
                      shift += 4;
                   dp--;
                }
                break;
             }
             default:
                break;
          }
          row_info->bit_depth = 8;
          row_info->pixel_depth = 8;
          row_info->rowbytes = row_width;
       }
       if (row_info->bit_depth == 8)
       {
          {
             if (num_trans > 0)
             {
                sp = row + (png_size_t)row_width - 1;
                dp = row + (png_size_t)(row_width << 2) - 1;
                for (i = 0; i < row_width; i++)
                {
                   if ((int)(*sp) >= num_trans)
                      *dp-- = 0xff;
                   else
                      *dp-- = trans_alpha[*sp];
                   *dp-- = palette[*sp].blue;
                   *dp-- = palette[*sp].green;
                   *dp-- = palette[*sp].red;
                   sp--;
                }
                row_info->bit_depth = 8;
                row_info->pixel_depth = 32;
                row_info->rowbytes = row_width * 4;
                row_info->color_type = 6;
                row_info->channels = 4;
             }
             else
             {
                sp = row + (png_size_t)row_width - 1;
                dp = row + (png_size_t)(row_width * 3) - 1;
                for (i = 0; i < row_width; i++)
                {
                   *dp-- = palette[*sp].blue;
                   *dp-- = palette[*sp].green;
                   *dp-- = palette[*sp].red;
                   sp--;
                }
                row_info->bit_depth = 8;
                row_info->pixel_depth = 24;
                row_info->rowbytes = row_width * 3;
                row_info->color_type = 2;
                row_info->channels = 3;
             }
          }
       }
    }
 }
 /* If the bit depth < 8, it is expanded to 8.  Also, if the already
  * expanded transparency value is supplied, an alpha channel is built.
  */
 static void
 png_do_expand(png_row_infop row_info, png_bytep row,
     png_const_color_16p trans_color)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
    png_debug(1, "in png_do_expand");
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          unsigned int gray = trans_color ? trans_color->gray : 0;
          if (row_info->bit_depth < 8)
          {
             switch (row_info->bit_depth)
             {
                case 1:
                {
                   gray = (gray & 0x01) * 0xff;
                   sp = row + (png_size_t)((row_width - 1) >> 3);
                   dp = row + (png_size_t)row_width - 1;
                   shift = 7 - (int)((row_width + 7) & 0x07);
                   for (i = 0; i < row_width; i++)
                   {
                      if ((*sp >> shift) & 0x01)
                         *dp = 0xff;
                      else
                         *dp = 0;
                      if (shift == 7)
                      {
                         shift = 0;
                         sp--;
                      }
                      else
                         shift++;
                      dp--;
                   }
                   break;
                }
                case 2:
                {
                   gray = (gray & 0x03) * 0x55;
                   sp = row + (png_size_t)((row_width - 1) >> 2);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                   for (i = 0; i < row_width; i++)
                   {
                      value = (*sp >> shift) & 0x03;
                      *dp = (png_byte)(value | (value << 2) | (value << 4) |
                         (value << 6));
                      if (shift == 6)
                      {
                         shift = 0;
                         sp--;
                      }
                      else
                         shift += 2;
                      dp--;
                   }
                   break;
                }
                case 4:
                {
                   gray = (gray & 0x0f) * 0x11;
                   sp = row + (png_size_t)((row_width - 1) >> 1);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
                   for (i = 0; i < row_width; i++)
                   {
                      value = (*sp >> shift) & 0x0f;
                      *dp = (png_byte)(value | (value << 4));
                      if (shift == 4)
                      {
                         shift = 0;
                         sp--;
                      }
                      else
                         shift = 4;
                      dp--;
                   }
                   break;
                }
                default:
                   break;
             }
             row_info->bit_depth = 8;
             row_info->pixel_depth = 8;
             row_info->rowbytes = row_width;
          }
          if (trans_color != NULL)
          {
             if (row_info->bit_depth == 8)
             {
                gray = gray & 0xff;
                sp = row + (png_size_t)row_width - 1;
                dp = row + (png_size_t)(row_width << 1) - 1;
                for (i = 0; i < row_width; i++)
                {
                   if (*sp == gray)
                      *dp-- = 0;
                   else
                      *dp-- = 0xff;
                   *dp-- = *sp--;
                }
             }
             else if (row_info->bit_depth == 16)
             {
                unsigned int gray_high = (gray >> 8) & 0xff;
                unsigned int gray_low = gray & 0xff;
                sp = row + row_info->rowbytes - 1;
                dp = row + (row_info->rowbytes << 1) - 1;
                for (i = 0; i < row_width; i++)
                {
                   if (*(sp - 1) == gray_high && *(sp) == gray_low)
                   {
                      *dp-- = 0;
                      *dp-- = 0;
                   }
                   else
                   {
                      *dp-- = 0xff;
                      *dp-- = 0xff;
                   }
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                }
             }
             row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
             row_info->channels = 2;
             row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
             row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
                row_width);
          }
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_color)
       {
          if (row_info->bit_depth == 8)
          {
             png_byte red = (png_byte)(trans_color->red & 0xff);
             png_byte green = (png_byte)(trans_color->green & 0xff);
             png_byte blue = (png_byte)(trans_color->blue & 0xff);
             sp = row + (png_size_t)row_info->rowbytes - 1;
             dp = row + (png_size_t)(row_width << 2) - 1;
             for (i = 0; i < row_width; i++)
             {
                if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
                   *dp-- = 0;
                else
                   *dp-- = 0xff;
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
             }
          }
          else if (row_info->bit_depth == 16)
          {
             png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
             png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
             png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
             png_byte red_low = (png_byte)(trans_color->red & 0xff);
             png_byte green_low = (png_byte)(trans_color->green & 0xff);
             png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
             sp = row + row_info->rowbytes - 1;
             dp = row + (png_size_t)(row_width << 3) - 1;
             for (i = 0; i < row_width; i++)
             {
                if (*(sp - 5) == red_high &&
                    *(sp - 4) == red_low &&
                    *(sp - 3) == green_high &&
                    *(sp - 2) == green_low &&
                    *(sp - 1) == blue_high &&
                    *(sp    ) == blue_low)
                {
                   *dp-- = 0;
                   *dp-- = 0;
                }
                else
                {
                   *dp-- = 0xff;
                   *dp-- = 0xff;
                }
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
             }
          }
          row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          row_info->channels = 4;
          row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
    }
 }
 #endif
 #ifdef PNG_READ_EXPAND_16_SUPPORTED
 /* If the bit depth is 8 and the color type is not a palette type expand the
  * whole row to 16 bits.  Has no effect otherwise.
  */
 static void
 png_do_expand_16(png_row_infop row_info, png_bytep row)
 {
    if (row_info->bit_depth == 8 &&
       row_info->color_type != PNG_COLOR_TYPE_PALETTE)
    {
       /* The row have a sequence of bytes containing [0..255] and we need
        * to turn it into another row containing [0..65535], to do this we
        * calculate:
        *
        *  (input / 255) * 65535
        *
        *  Which happens to be exactly input * 257 and this can be achieved
        *  simply by byte replication in place (copying backwards).
        */
       png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
       png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
       while (dp > sp)
          dp[-2] = dp[-1] = *--sp, dp -= 2;
       row_info->rowbytes *= 2;
       row_info->bit_depth = 16;
       row_info->pixel_depth = (png_byte)(row_info->channels * 16);
    }
 }
 #endif
 #ifdef PNG_READ_QUANTIZE_SUPPORTED
 static void
 png_do_quantize(png_row_infop row_info, png_bytep row,
     png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
 {
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
    png_debug(1, "in png_do_quantize");
    if (row_info->bit_depth == 8)
    {
       if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
       {
          int r, g, b, p;
          sp = row;
          dp = row;
          for (i = 0; i < row_width; i++)
          {
             r = *sp++;
             g = *sp++;
             b = *sp++;
             /* This looks real messy, but the compiler will reduce
              * it down to a reasonable formula.  For example, with
              * 5 bits per color, we get:
              * p = (((r >> 3) & 0x1f) << 10) |
              *    (((g >> 3) & 0x1f) << 5) |
              *    ((b >> 3) & 0x1f);
              */
             p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                 ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                 (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                 (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                 ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                 (PNG_QUANTIZE_BLUE_BITS)) |
                 ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                 ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
             *dp++ = palette_lookup[p];
          }
          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
          row_info->channels = 1;
          row_info->pixel_depth = row_info->bit_depth;
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
          palette_lookup != NULL)
       {
          int r, g, b, p;
          sp = row;
          dp = row;
          for (i = 0; i < row_width; i++)
          {
             r = *sp++;
             g = *sp++;
             b = *sp++;
             sp++;
             p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                 ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                 (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                 (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                 ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                 (PNG_QUANTIZE_BLUE_BITS)) |
                 ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                 ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
             *dp++ = palette_lookup[p];
          }
          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
          row_info->channels = 1;
          row_info->pixel_depth = row_info->bit_depth;
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
          quantize_lookup)
       {
          sp = row;
          for (i = 0; i < row_width; i++, sp++)
          {
             *sp = quantize_lookup[*sp];
          }
       }
    }
 }
 #endif /* PNG_READ_QUANTIZE_SUPPORTED */
 /* Transform the row.  The order of transformations is significant,
  * and is very touchy.  If you add a transformation, take care to
  * decide how it fits in with the other transformations here.
  */
 void /* PRIVATE */
 png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
 {
    png_debug(1, "in png_do_read_transformations");
    if (png_ptr->row_buf == NULL)
    {
       /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
        * error is incredibly rare and incredibly easy to debug without this
        * information.
        */
       png_error(png_ptr, "NULL row buffer");
    }
    /* The following is debugging; prior to 1.5.4 the code was never compiled in;
     * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
     * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.6 the new flag is set only for
     * all transformations, however in practice the ROW_INIT always gets done on
     * demand, if necessary.
     */
    if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
       !(png_ptr->flags & PNG_FLAG_ROW_INIT))
    {
       /* Application has failed to call either png_read_start_image() or
        * png_read_update_info() after setting transforms that expand pixels.
        * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
        */
       png_error(png_ptr, "Uninitialized row");
    }
 #ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
       if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          png_do_expand_palette(row_info, png_ptr->row_buf + 1,
              png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
       }
       else
       {
          if (png_ptr->num_trans &&
              (png_ptr->transformations & PNG_EXPAND_tRNS))
             png_do_expand(row_info, png_ptr->row_buf + 1,
                 &(png_ptr->trans_color));
          else
             png_do_expand(row_info, png_ptr->row_buf + 1,
                 NULL);
       }
    }
 #endif
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
       !(png_ptr->transformations & PNG_COMPOSE) &&
       (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
       row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
       png_do_strip_channel(row_info, png_ptr->row_buf + 1,
 /* at_start == false, because SWAP_ALPHA happens later */);
 #endif
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
    {
       int rgb_error =
           png_do_rgb_to_gray(png_ptr, row_info,
               png_ptr->row_buf + 1);
       if (rgb_error)
       {
          png_ptr->rgb_to_gray_status=1;
          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
              PNG_RGB_TO_GRAY_WARN)
             png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
              PNG_RGB_TO_GRAY_ERR)
             png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
       }
    }
 #endif
 /* From Andreas Dilger e-mail to png-implement, 26 March 1998:
  *
  *   In most cases, the "simple transparency" should be done prior to doing
  *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
  *   pixel is transparent.  You would also need to make sure that the
  *   transparency information is upgraded to RGB.
  *
  *   To summarize, the current flow is:
  *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
  *                                   with background "in place" if transparent,
  *                                   convert to RGB if necessary
  *   - Gray + alpha -> composite with gray background and remove alpha bytes,
  *                                   convert to RGB if necessary
  *
  *   To support RGB backgrounds for gray images we need:
  *   - Gray + simple transparency -> convert to RGB + simple transparency,
  *                                   compare 3 or 6 bytes and composite with
  *                                   background "in place" if transparent
  *                                   (3x compare/pixel compared to doing
  *                                   composite with gray bkgrnd)
  *   - Gray + alpha -> convert to RGB + alpha, composite with background and
  *                                   remove alpha bytes (3x float
  *                                   operations/pixel compared with composite
  *                                   on gray background)
  *
  *  Greg's change will do this.  The reason it wasn't done before is for
  *  performance, as this increases the per-pixel operations.  If we would check
  *  in advance if the background was gray or RGB, and position the gray-to-RGB
  *  transform appropriately, then it would save a lot of work/time.
  */
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* If gray -> RGB, do so now only if background is non-gray; else do later
     * for performance reasons
     */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
       png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
 #endif
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
    if (png_ptr->transformations & PNG_COMPOSE)
       png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
 #endif
 #ifdef PNG_READ_GAMMA_SUPPORTED
    if ((png_ptr->transformations & PNG_GAMMA) &&
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
       /* Because RGB_TO_GRAY does the gamma transform. */
       !(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
 #endif
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
       /* Because PNG_COMPOSE does the gamma transform if there is something to
        * do (if there is an alpha channel or transparency.)
        */
        !((png_ptr->transformations & PNG_COMPOSE) &&
        ((png_ptr->num_trans != 0) ||
        (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
 #endif
       /* Because png_init_read_transformations transforms the palette, unless
        * RGB_TO_GRAY will do the transform.
        */
        (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
       png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
 #endif
 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
       (png_ptr->transformations & PNG_COMPOSE) &&
       (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
       row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
       png_do_strip_channel(row_info, png_ptr->row_buf + 1,
 /* at_start == false, because SWAP_ALPHA happens later */);
 #endif
 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
    if ((png_ptr->transformations & PNG_ENCODE_ALPHA) &&
       (row_info->color_type & PNG_COLOR_MASK_ALPHA))
       png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
 #endif
 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
    if (png_ptr->transformations & PNG_SCALE_16_TO_8)
       png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
    /* There is no harm in doing both of these because only one has any effect,
     * by putting the 'scale' option first if the app asks for scale (either by
     * calling the API or in a TRANSFORM flag) this is what happens.
     */
    if (png_ptr->transformations & PNG_16_TO_8)
       png_do_chop(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_QUANTIZE_SUPPORTED
    if (png_ptr->transformations & PNG_QUANTIZE)
    {
       png_do_quantize(row_info, png_ptr->row_buf + 1,
           png_ptr->palette_lookup, png_ptr->quantize_index);
       if (row_info->rowbytes == 0)
          png_error(png_ptr, "png_do_quantize returned rowbytes=0");
    }
 #endif /* PNG_READ_QUANTIZE_SUPPORTED */
 #ifdef PNG_READ_EXPAND_16_SUPPORTED
    /* Do the expansion now, after all the arithmetic has been done.  Notice
     * that previous transformations can handle the PNG_EXPAND_16 flag if this
     * is efficient (particularly true in the case of gamma correction, where
     * better accuracy results faster!)
     */
    if (png_ptr->transformations & PNG_EXPAND_16)
       png_do_expand_16(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* NOTE: moved here in 1.5.4 (from much later in this list.) */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
       png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_INVERT_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_MONO)
       png_do_invert(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_ALPHA)
       png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_SHIFT_SUPPORTED
    if (png_ptr->transformations & PNG_SHIFT)
       png_do_unshift(row_info, png_ptr->row_buf + 1,
           &(png_ptr->shift));
 #endif
 #ifdef PNG_READ_PACK_SUPPORTED
    if (png_ptr->transformations & PNG_PACK)
       png_do_unpack(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
    /* Added at libpng-1.5.10 */
    if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
        png_ptr->num_palette_max >= 0)
       png_do_check_palette_indexes(png_ptr, row_info);
 #endif
 #ifdef PNG_READ_BGR_SUPPORTED
    if (png_ptr->transformations & PNG_BGR)
       png_do_bgr(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_PACKSWAP_SUPPORTED
    if (png_ptr->transformations & PNG_PACKSWAP)
       png_do_packswap(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_FILLER_SUPPORTED
    if (png_ptr->transformations & PNG_FILLER)
       png_do_read_filler(row_info, png_ptr->row_buf + 1,
           (png_uint_32)png_ptr->filler, png_ptr->flags);
 #endif
 #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_ALPHA)
       png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
 #endif
 #ifdef PNG_READ_16BIT_SUPPORTED
 #ifdef PNG_READ_SWAP_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_BYTES)
       png_do_swap(row_info, png_ptr->row_buf + 1);
 #endif
 #endif
 #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
     {
       if (png_ptr->read_user_transform_fn != NULL)
          (*(png_ptr->read_user_transform_fn)) /* User read transform function */
              (png_ptr,     /* png_ptr */
              row_info,     /* row_info: */
                 /*  png_uint_32 width;       width of row */
                 /*  png_size_t rowbytes;     number of bytes in row */
                 /*  png_byte color_type;     color type of pixels */
                 /*  png_byte bit_depth;      bit depth of samples */
                 /*  png_byte channels;       number of channels (1-4) */
                 /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
              png_ptr->row_buf + 1);    /* start of pixel data for row */
 #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
       if (png_ptr->user_transform_depth)
          row_info->bit_depth = png_ptr->user_transform_depth;
       if (png_ptr->user_transform_channels)
          row_info->channels = png_ptr->user_transform_channels;
 #endif
       row_info->pixel_depth = (png_byte)(row_info->bit_depth *
           row_info->channels);
       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
    }
 #endif
 }
 #endif /* PNG_READ_TRANSFORMS_SUPPORTED */
 #endif /* PNG_READ_SUPPORTED */

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media/libpng/pngrtran.c@97036ab72558 (annotated)

media/libpng/pngrtran.c