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 /* pngread.c - read a PNG file

  *

  * 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 routines that an application calls directly to

  * read a PNG file or stream.

  */

 #include "pngpriv.h"

 #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)

 #  include <errno.h>

 #endif

 #ifdef PNG_READ_SUPPORTED

 /* Create a PNG structure for reading, and allocate any memory needed. */

 PNG_FUNCTION(png_structp,PNGAPI

 png_create_read_struct,(png_const_charp user_png_ver, png_voidp error_ptr,

     png_error_ptr error_fn, png_error_ptr warn_fn),PNG_ALLOCATED)

 {

 #ifndef PNG_USER_MEM_SUPPORTED

    png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,

       error_fn, warn_fn, NULL, NULL, NULL);

 #else

    return png_create_read_struct_2(user_png_ver, error_ptr, error_fn,

        warn_fn, NULL, NULL, NULL);

 }

 /* Alternate create PNG structure for reading, and allocate any memory

  * needed.

  */

 PNG_FUNCTION(png_structp,PNGAPI

 png_create_read_struct_2,(png_const_charp user_png_ver, png_voidp error_ptr,

     png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,

     png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)

 {

    png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,

       error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);

 #endif /* PNG_USER_MEM_SUPPORTED */

    if (png_ptr != NULL)

    {

       png_ptr->mode = PNG_IS_READ_STRUCT;

       /* Added in libpng-1.6.0; this can be used to detect a read structure if

        * required (it will be zero in a write structure.)

        */

 #     ifdef PNG_SEQUENTIAL_READ_SUPPORTED

          png_ptr->IDAT_read_size = PNG_IDAT_READ_SIZE;

 #     endif

 #     ifdef PNG_BENIGN_READ_ERRORS_SUPPORTED

          png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;

          /* In stable builds only warn if an application error can be completely

           * handled.

           */

 #        if PNG_LIBPNG_BUILD_BASE_TYPE >= PNG_LIBPNG_BUILD_RC

             png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;

 #        endif

 #     endif

       /* TODO: delay this, it can be done in png_init_io (if the app doesn't

        * do it itself) avoiding setting the default function if it is not

        * required.

        */

       png_set_read_fn(png_ptr, NULL, NULL);

    }

    return png_ptr;

 }

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 /* Read the information before the actual image data.  This has been

  * changed in v0.90 to allow reading a file that already has the magic

  * bytes read from the stream.  You can tell libpng how many bytes have

  * been read from the beginning of the stream (up to the maximum of 8)

  * via png_set_sig_bytes(), and we will only check the remaining bytes

  * here.  The application can then have access to the signature bytes we

  * read if it is determined that this isn't a valid PNG file.

  */

 void PNGAPI

 png_read_info(png_structrp png_ptr, png_inforp info_ptr)

 {

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

    int keep;

 #endif

    png_debug(1, "in png_read_info");

    if (png_ptr == NULL || info_ptr == NULL)

       return;

    /* Read and check the PNG file signature. */

    png_read_sig(png_ptr, info_ptr);

    for (;;)

    {

       png_uint_32 length = png_read_chunk_header(png_ptr);

       png_uint_32 chunk_name = png_ptr->chunk_name;

       /* IDAT logic needs to happen here to simplify getting the two flags

        * right.

        */

       if (chunk_name == png_IDAT)

       {

          if (!(png_ptr->mode & PNG_HAVE_IHDR))

             png_chunk_error(png_ptr, "Missing IHDR before IDAT");

          else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&

              !(png_ptr->mode & PNG_HAVE_PLTE))

             png_chunk_error(png_ptr, "Missing PLTE before IDAT");

          else if (png_ptr->mode & PNG_AFTER_IDAT)

             png_chunk_benign_error(png_ptr, "Too many IDATs found");

          png_ptr->mode |= PNG_HAVE_IDAT;

       }

       else if (png_ptr->mode & PNG_HAVE_IDAT)

          png_ptr->mode |= PNG_AFTER_IDAT;

       /* This should be a binary subdivision search or a hash for

        * matching the chunk name rather than a linear search.

        */

       if (chunk_name == png_IHDR)

          png_handle_IHDR(png_ptr, info_ptr, length);

       else if (chunk_name == png_IEND)

          png_handle_IEND(png_ptr, info_ptr, length);

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

       else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)

       {

          png_handle_unknown(png_ptr, info_ptr, length, keep);

          if (chunk_name == png_PLTE)

             png_ptr->mode |= PNG_HAVE_PLTE;

          else if (chunk_name == png_IDAT)

          {

             png_ptr->idat_size = 0; /* It has been consumed */

             break;

          }

       }

 #endif

       else if (chunk_name == png_PLTE)

          png_handle_PLTE(png_ptr, info_ptr, length);

       else if (chunk_name == png_IDAT)

       {

 #ifdef PNG_READ_APNG_SUPPORTED

          png_have_info(png_ptr, info_ptr);

 #endif

          png_ptr->idat_size = length;

          break;

       }

 #ifdef PNG_READ_bKGD_SUPPORTED

       else if (chunk_name == png_bKGD)

          png_handle_bKGD(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_cHRM_SUPPORTED

       else if (chunk_name == png_cHRM)

          png_handle_cHRM(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_gAMA_SUPPORTED

       else if (chunk_name == png_gAMA)

          png_handle_gAMA(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_hIST_SUPPORTED

       else if (chunk_name == png_hIST)

          png_handle_hIST(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_oFFs_SUPPORTED

       else if (chunk_name == png_oFFs)

          png_handle_oFFs(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_pCAL_SUPPORTED

       else if (chunk_name == png_pCAL)

          png_handle_pCAL(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sCAL_SUPPORTED

       else if (chunk_name == png_sCAL)

          png_handle_sCAL(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_pHYs_SUPPORTED

       else if (chunk_name == png_pHYs)

          png_handle_pHYs(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sBIT_SUPPORTED

       else if (chunk_name == png_sBIT)

          png_handle_sBIT(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sRGB_SUPPORTED

       else if (chunk_name == png_sRGB)

          png_handle_sRGB(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_iCCP_SUPPORTED

       else if (chunk_name == png_iCCP)

          png_handle_iCCP(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sPLT_SUPPORTED

       else if (chunk_name == png_sPLT)

          png_handle_sPLT(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tEXt_SUPPORTED

       else if (chunk_name == png_tEXt)

          png_handle_tEXt(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tIME_SUPPORTED

       else if (chunk_name == png_tIME)

          png_handle_tIME(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tRNS_SUPPORTED

       else if (chunk_name == png_tRNS)

          png_handle_tRNS(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_zTXt_SUPPORTED

       else if (chunk_name == png_zTXt)

          png_handle_zTXt(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_iTXt_SUPPORTED

       else if (chunk_name == png_iTXt)

          png_handle_iTXt(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_APNG_SUPPORTED

       else if (chunk_name == png_acTL)

          png_handle_acTL(png_ptr, info_ptr, length);

       else if (chunk_name == png_fcTL)

          png_handle_fcTL(png_ptr, info_ptr, length);

       else if (chunk_name == png_fdAT)

          png_handle_fdAT(png_ptr, info_ptr, length);

 #endif

       else

          png_handle_unknown(png_ptr, info_ptr, length,

             PNG_HANDLE_CHUNK_AS_DEFAULT);

    }

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_READ_APNG_SUPPORTED

 void PNGAPI

 png_read_frame_head(png_structp png_ptr, png_infop info_ptr)

 {

     png_byte have_chunk_after_DAT; /* after IDAT or after fdAT */

     png_debug(0, "Reading frame head");

     if (!(png_ptr->mode & PNG_HAVE_acTL))

         png_error(png_ptr, "attempt to png_read_frame_head() but "

                            "no acTL present");

     /* do nothing for the main IDAT */

     if (png_ptr->num_frames_read == 0)

         return;

     png_read_reset(png_ptr);

     png_ptr->flags &= ~PNG_FLAG_ROW_INIT;

     png_ptr->mode &= ~PNG_HAVE_fcTL;

     have_chunk_after_DAT = 0;

     for (;;)

     {

         png_uint_32 length = png_read_chunk_header(png_ptr);

         if (png_ptr->chunk_name == png_IDAT)

         {

             /* discard trailing IDATs for the first frame */

             if (have_chunk_after_DAT || png_ptr->num_frames_read > 1)

                 png_error(png_ptr, "png_read_frame_head(): out of place IDAT");

             png_crc_finish(png_ptr, length);

         }

         else if (png_ptr->chunk_name == png_fcTL)

         {

             png_handle_fcTL(png_ptr, info_ptr, length);

             have_chunk_after_DAT = 1;

         }

         else if (png_ptr->chunk_name == png_fdAT)

         {

             png_ensure_sequence_number(png_ptr, length);

             /* discard trailing fdATs for frames other than the first */

             if (!have_chunk_after_DAT && png_ptr->num_frames_read > 1)

                 png_crc_finish(png_ptr, length - 4);

             else if(png_ptr->mode & PNG_HAVE_fcTL)

             {

                 png_ptr->idat_size = length - 4;

                 png_ptr->mode |= PNG_HAVE_IDAT;

                 break;

             }

             else

                 png_error(png_ptr, "png_read_frame_head(): out of place fdAT");

         }

         else

         {

             png_warning(png_ptr, "Skipped (ignored) a chunk "

                                  "between APNG chunks");

             png_crc_finish(png_ptr, length);

         }

     }

 }

 #endif /* PNG_READ_APNG_SUPPORTED */

 /* Optional call to update the users info_ptr structure */

 void PNGAPI

 png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)

 {

    png_debug(1, "in png_read_update_info");

    if (png_ptr != NULL)

    {

       if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)

       {

          png_read_start_row(png_ptr);

 #        ifdef PNG_READ_TRANSFORMS_SUPPORTED

             png_read_transform_info(png_ptr, info_ptr);

 #        else

             PNG_UNUSED(info_ptr)

 #        endif

       }

       /* New in 1.6.0 this avoids the bug of doing the initializations twice */

       else

          png_app_error(png_ptr,

             "png_read_update_info/png_start_read_image: duplicate call");

    }

 }

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 /* Initialize palette, background, etc, after transformations

  * are set, but before any reading takes place.  This allows

  * the user to obtain a gamma-corrected palette, for example.

  * If the user doesn't call this, we will do it ourselves.

  */

 void PNGAPI

 png_start_read_image(png_structrp png_ptr)

 {

    png_debug(1, "in png_start_read_image");

    if (png_ptr != NULL)

    {

       if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)

          png_read_start_row(png_ptr);

       /* New in 1.6.0 this avoids the bug of doing the initializations twice */

       else

          png_app_error(png_ptr,

             "png_start_read_image/png_read_update_info: duplicate call");

    }

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 #ifdef PNG_MNG_FEATURES_SUPPORTED

 /* Undoes intrapixel differencing,

  * NOTE: this is apparently only supported in the 'sequential' reader.

  */

 static void

 png_do_read_intrapixel(png_row_infop row_info, png_bytep row)

 {

    png_debug(1, "in png_do_read_intrapixel");

    if (

        (row_info->color_type & PNG_COLOR_MASK_COLOR))

    {

       int bytes_per_pixel;

       png_uint_32 row_width = row_info->width;

       if (row_info->bit_depth == 8)

       {

          png_bytep rp;

          png_uint_32 i;

          if (row_info->color_type == PNG_COLOR_TYPE_RGB)

             bytes_per_pixel = 3;

          else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)

             bytes_per_pixel = 4;

          else

             return;

          for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)

          {

             *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);

             *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);

          }

       }

       else if (row_info->bit_depth == 16)

       {

          png_bytep rp;

          png_uint_32 i;

          if (row_info->color_type == PNG_COLOR_TYPE_RGB)

             bytes_per_pixel = 6;

          else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)

             bytes_per_pixel = 8;

          else

             return;

          for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)

          {

             png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);

             png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);

             png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);

             png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;

             png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;

             *(rp    ) = (png_byte)((red >> 8) & 0xff);

             *(rp + 1) = (png_byte)(red & 0xff);

             *(rp + 4) = (png_byte)((blue >> 8) & 0xff);

             *(rp + 5) = (png_byte)(blue & 0xff);

          }

       }

    }

 }

 #endif /* PNG_MNG_FEATURES_SUPPORTED */

 void PNGAPI

 png_read_row(png_structrp png_ptr, png_bytep row, png_bytep dsp_row)

 {

    png_row_info row_info;

    if (png_ptr == NULL)

       return;

    png_debug2(1, "in png_read_row (row %lu, pass %d)",

        (unsigned long)png_ptr->row_number, png_ptr->pass);

    /* png_read_start_row sets the information (in particular iwidth) for this

     * interlace pass.

     */

    if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))

       png_read_start_row(png_ptr);

    /* 1.5.6: row_info moved out of png_struct to a local here. */

    row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */

    row_info.color_type = png_ptr->color_type;

    row_info.bit_depth = png_ptr->bit_depth;

    row_info.channels = png_ptr->channels;

    row_info.pixel_depth = png_ptr->pixel_depth;

    row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);

    if (png_ptr->row_number == 0 && png_ptr->pass == 0)

    {

    /* Check for transforms that have been set but were defined out */

 #if defined(PNG_WRITE_INVERT_SUPPORTED) && !defined(PNG_READ_INVERT_SUPPORTED)

    if (png_ptr->transformations & PNG_INVERT_MONO)

       png_warning(png_ptr, "PNG_READ_INVERT_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_FILLER_SUPPORTED) && !defined(PNG_READ_FILLER_SUPPORTED)

    if (png_ptr->transformations & PNG_FILLER)

       png_warning(png_ptr, "PNG_READ_FILLER_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \

     !defined(PNG_READ_PACKSWAP_SUPPORTED)

    if (png_ptr->transformations & PNG_PACKSWAP)

       png_warning(png_ptr, "PNG_READ_PACKSWAP_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_PACK_SUPPORTED) && !defined(PNG_READ_PACK_SUPPORTED)

    if (png_ptr->transformations & PNG_PACK)

       png_warning(png_ptr, "PNG_READ_PACK_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_SHIFT_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED)

    if (png_ptr->transformations & PNG_SHIFT)

       png_warning(png_ptr, "PNG_READ_SHIFT_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_BGR_SUPPORTED) && !defined(PNG_READ_BGR_SUPPORTED)

    if (png_ptr->transformations & PNG_BGR)

       png_warning(png_ptr, "PNG_READ_BGR_SUPPORTED is not defined");

 #endif

 #if defined(PNG_WRITE_SWAP_SUPPORTED) && !defined(PNG_READ_SWAP_SUPPORTED)

    if (png_ptr->transformations & PNG_SWAP_BYTES)

       png_warning(png_ptr, "PNG_READ_SWAP_SUPPORTED is not defined");

 #endif

    }

 #ifdef PNG_READ_INTERLACING_SUPPORTED

    /* If interlaced and we do not need a new row, combine row and return.

     * Notice that the pixels we have from previous rows have been transformed

     * already; we can only combine like with like (transformed or

     * untransformed) and, because of the libpng API for interlaced images, this

     * means we must transform before de-interlacing.

     */

    if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))

    {

       switch (png_ptr->pass)

       {

          case 0:

             if (png_ptr->row_number & 0x07)

             {

                if (dsp_row != NULL)

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          case 1:

             if ((png_ptr->row_number & 0x07) || png_ptr->width < 5)

             {

                if (dsp_row != NULL)

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          case 2:

             if ((png_ptr->row_number & 0x07) != 4)

             {

                if (dsp_row != NULL && (png_ptr->row_number & 4))

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          case 3:

             if ((png_ptr->row_number & 3) || png_ptr->width < 3)

             {

                if (dsp_row != NULL)

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          case 4:

             if ((png_ptr->row_number & 3) != 2)

             {

                if (dsp_row != NULL && (png_ptr->row_number & 2))

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          case 5:

             if ((png_ptr->row_number & 1) || png_ptr->width < 2)

             {

                if (dsp_row != NULL)

                   png_combine_row(png_ptr, dsp_row, 1/*display*/);

                png_read_finish_row(png_ptr);

                return;

             }

             break;

          default:

          case 6:

             if (!(png_ptr->row_number & 1))

             {

                png_read_finish_row(png_ptr);

                return;

             }

             break;

       }

    }

 #endif

    if (!(png_ptr->mode & PNG_HAVE_IDAT))

       png_error(png_ptr, "Invalid attempt to read row data");

    /* Fill the row with IDAT data: */

    png_read_IDAT_data(png_ptr, png_ptr->row_buf, row_info.rowbytes + 1);

    if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)

    {

       if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)

          png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,

             png_ptr->prev_row + 1, png_ptr->row_buf[0]);

       else

          png_error(png_ptr, "bad adaptive filter value");

    }

    /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before

     * 1.5.6, while the buffer really is this big in current versions of libpng

     * it may not be in the future, so this was changed just to copy the

     * interlaced count:

     */

    memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);

 #ifdef PNG_MNG_FEATURES_SUPPORTED

    if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&

        (png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING))

    {

       /* Intrapixel differencing */

       png_do_read_intrapixel(&row_info, png_ptr->row_buf + 1);

    }

 #endif

 #ifdef PNG_READ_TRANSFORMS_SUPPORTED

    if (png_ptr->transformations)

       png_do_read_transformations(png_ptr, &row_info);

 #endif

    /* The transformed pixel depth should match the depth now in row_info. */

    if (png_ptr->transformed_pixel_depth == 0)

    {

       png_ptr->transformed_pixel_depth = row_info.pixel_depth;

       if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)

          png_error(png_ptr, "sequential row overflow");

    }

    else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)

       png_error(png_ptr, "internal sequential row size calculation error");

 #ifdef PNG_READ_INTERLACING_SUPPORTED

    /* Blow up interlaced rows to full size */

    if (png_ptr->interlaced &&

       (png_ptr->transformations & PNG_INTERLACE))

    {

       if (png_ptr->pass < 6)

          png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,

             png_ptr->transformations);

       if (dsp_row != NULL)

          png_combine_row(png_ptr, dsp_row, 1/*display*/);

       if (row != NULL)

          png_combine_row(png_ptr, row, 0/*row*/);

    }

    else

 #endif

    {

       if (row != NULL)

          png_combine_row(png_ptr, row, -1/*ignored*/);

       if (dsp_row != NULL)

          png_combine_row(png_ptr, dsp_row, -1/*ignored*/);

    }

    png_read_finish_row(png_ptr);

    if (png_ptr->read_row_fn != NULL)

       (*(png_ptr->read_row_fn))(png_ptr, png_ptr->row_number, png_ptr->pass);

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 /* Read one or more rows of image data.  If the image is interlaced,

  * and png_set_interlace_handling() has been called, the rows need to

  * contain the contents of the rows from the previous pass.  If the

  * image has alpha or transparency, and png_handle_alpha()[*] has been

  * called, the rows contents must be initialized to the contents of the

  * screen.

  *

  * "row" holds the actual image, and pixels are placed in it

  * as they arrive.  If the image is displayed after each pass, it will

  * appear to "sparkle" in.  "display_row" can be used to display a

  * "chunky" progressive image, with finer detail added as it becomes

  * available.  If you do not want this "chunky" display, you may pass

  * NULL for display_row.  If you do not want the sparkle display, and

  * you have not called png_handle_alpha(), you may pass NULL for rows.

  * If you have called png_handle_alpha(), and the image has either an

  * alpha channel or a transparency chunk, you must provide a buffer for

  * rows.  In this case, you do not have to provide a display_row buffer

  * also, but you may.  If the image is not interlaced, or if you have

  * not called png_set_interlace_handling(), the display_row buffer will

  * be ignored, so pass NULL to it.

  *

  * [*] png_handle_alpha() does not exist yet, as of this version of libpng

  */

 void PNGAPI

 png_read_rows(png_structrp png_ptr, png_bytepp row,

     png_bytepp display_row, png_uint_32 num_rows)

 {

    png_uint_32 i;

    png_bytepp rp;

    png_bytepp dp;

    png_debug(1, "in png_read_rows");

    if (png_ptr == NULL)

       return;

    rp = row;

    dp = display_row;

    if (rp != NULL && dp != NULL)

       for (i = 0; i < num_rows; i++)

       {

          png_bytep rptr = *rp++;

          png_bytep dptr = *dp++;

          png_read_row(png_ptr, rptr, dptr);

       }

    else if (rp != NULL)

       for (i = 0; i < num_rows; i++)

       {

          png_bytep rptr = *rp;

          png_read_row(png_ptr, rptr, NULL);

          rp++;

       }

    else if (dp != NULL)

       for (i = 0; i < num_rows; i++)

       {

          png_bytep dptr = *dp;

          png_read_row(png_ptr, NULL, dptr);

          dp++;

       }

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 /* Read the entire image.  If the image has an alpha channel or a tRNS

  * chunk, and you have called png_handle_alpha()[*], you will need to

  * initialize the image to the current image that PNG will be overlaying.

  * We set the num_rows again here, in case it was incorrectly set in

  * png_read_start_row() by a call to png_read_update_info() or

  * png_start_read_image() if png_set_interlace_handling() wasn't called

  * prior to either of these functions like it should have been.  You can

  * only call this function once.  If you desire to have an image for

  * each pass of a interlaced image, use png_read_rows() instead.

  *

  * [*] png_handle_alpha() does not exist yet, as of this version of libpng

  */

 void PNGAPI

 png_read_image(png_structrp png_ptr, png_bytepp image)

 {

    png_uint_32 i, image_height;

    int pass, j;

    png_bytepp rp;

    png_debug(1, "in png_read_image");

    if (png_ptr == NULL)

       return;

 #ifdef PNG_READ_INTERLACING_SUPPORTED

    if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))

    {

       pass = png_set_interlace_handling(png_ptr);

       /* And make sure transforms are initialized. */

       png_start_read_image(png_ptr);

    }

    else

    {

       if (png_ptr->interlaced && !(png_ptr->transformations & PNG_INTERLACE))

       {

          /* Caller called png_start_read_image or png_read_update_info without

           * first turning on the PNG_INTERLACE transform.  We can fix this here,

           * but the caller should do it!

           */

          png_warning(png_ptr, "Interlace handling should be turned on when "

             "using png_read_image");

          /* Make sure this is set correctly */

          png_ptr->num_rows = png_ptr->height;

       }

       /* Obtain the pass number, which also turns on the PNG_INTERLACE flag in

        * the above error case.

        */

       pass = png_set_interlace_handling(png_ptr);

    }

 #else

    if (png_ptr->interlaced)

       png_error(png_ptr,

           "Cannot read interlaced image -- interlace handler disabled");

    pass = 1;

 #endif

    image_height=png_ptr->height;

    for (j = 0; j < pass; j++)

    {

       rp = image;

       for (i = 0; i < image_height; i++)

       {

          png_read_row(png_ptr, *rp, NULL);

          rp++;

       }

    }

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 /* Read the end of the PNG file.  Will not read past the end of the

  * file, will verify the end is accurate, and will read any comments

  * or time information at the end of the file, if info is not NULL.

  */

 void PNGAPI

 png_read_end(png_structrp png_ptr, png_inforp info_ptr)

 {

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

    int keep;

 #endif

    png_debug(1, "in png_read_end");

    if (png_ptr == NULL)

       return;

    /* If png_read_end is called in the middle of reading the rows there may

     * still be pending IDAT data and an owned zstream.  Deal with this here.

     */

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

    if (!png_chunk_unknown_handling(png_ptr, png_IDAT))

 #endif

       png_read_finish_IDAT(png_ptr);

 #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED

    /* Report invalid palette index; added at libng-1.5.10 */

    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&

       png_ptr->num_palette_max > png_ptr->num_palette)

      png_benign_error(png_ptr, "Read palette index exceeding num_palette");

 #endif

    do

    {

       png_uint_32 length = png_read_chunk_header(png_ptr);

       png_uint_32 chunk_name = png_ptr->chunk_name;

       if (chunk_name == png_IEND)

          png_handle_IEND(png_ptr, info_ptr, length);

       else if (chunk_name == png_IHDR)

          png_handle_IHDR(png_ptr, info_ptr, length);

       else if (info_ptr == NULL)

          png_crc_finish(png_ptr, length);

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

       else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)

       {

          if (chunk_name == png_IDAT)

          {

             if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))

                png_benign_error(png_ptr, "Too many IDATs found");

          }

          png_handle_unknown(png_ptr, info_ptr, length, keep);

          if (chunk_name == png_PLTE)

             png_ptr->mode |= PNG_HAVE_PLTE;

       }

 #endif

       else if (chunk_name == png_IDAT)

       {

          /* Zero length IDATs are legal after the last IDAT has been

           * read, but not after other chunks have been read.

           */

          if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))

             png_benign_error(png_ptr, "Too many IDATs found");

          png_crc_finish(png_ptr, length);

       }

       else if (chunk_name == png_PLTE)

          png_handle_PLTE(png_ptr, info_ptr, length);

 #ifdef PNG_READ_bKGD_SUPPORTED

       else if (chunk_name == png_bKGD)

          png_handle_bKGD(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_cHRM_SUPPORTED

       else if (chunk_name == png_cHRM)

          png_handle_cHRM(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_gAMA_SUPPORTED

       else if (chunk_name == png_gAMA)

          png_handle_gAMA(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_hIST_SUPPORTED

       else if (chunk_name == png_hIST)

          png_handle_hIST(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_oFFs_SUPPORTED

       else if (chunk_name == png_oFFs)

          png_handle_oFFs(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_pCAL_SUPPORTED

       else if (chunk_name == png_pCAL)

          png_handle_pCAL(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sCAL_SUPPORTED

       else if (chunk_name == png_sCAL)

          png_handle_sCAL(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_pHYs_SUPPORTED

       else if (chunk_name == png_pHYs)

          png_handle_pHYs(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sBIT_SUPPORTED

       else if (chunk_name == png_sBIT)

          png_handle_sBIT(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sRGB_SUPPORTED

       else if (chunk_name == png_sRGB)

          png_handle_sRGB(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_iCCP_SUPPORTED

       else if (chunk_name == png_iCCP)

          png_handle_iCCP(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_sPLT_SUPPORTED

       else if (chunk_name == png_sPLT)

          png_handle_sPLT(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tEXt_SUPPORTED

       else if (chunk_name == png_tEXt)

          png_handle_tEXt(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tIME_SUPPORTED

       else if (chunk_name == png_tIME)

          png_handle_tIME(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_tRNS_SUPPORTED

       else if (chunk_name == png_tRNS)

          png_handle_tRNS(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_zTXt_SUPPORTED

       else if (chunk_name == png_zTXt)

          png_handle_zTXt(png_ptr, info_ptr, length);

 #endif

 #ifdef PNG_READ_iTXt_SUPPORTED

       else if (chunk_name == png_iTXt)

          png_handle_iTXt(png_ptr, info_ptr, length);

 #endif

       else

          png_handle_unknown(png_ptr, info_ptr, length,

             PNG_HANDLE_CHUNK_AS_DEFAULT);

    } while (!(png_ptr->mode & PNG_HAVE_IEND));

 }

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 /* Free all memory used in the read struct */

 static void

 png_read_destroy(png_structrp png_ptr)

 {

    png_debug(1, "in png_read_destroy");

 #ifdef PNG_READ_GAMMA_SUPPORTED

    png_destroy_gamma_table(png_ptr);

 #endif

    png_free(png_ptr, png_ptr->big_row_buf);

    png_free(png_ptr, png_ptr->big_prev_row);

    png_free(png_ptr, png_ptr->read_buffer);

 #ifdef PNG_READ_QUANTIZE_SUPPORTED

    png_free(png_ptr, png_ptr->palette_lookup);

    png_free(png_ptr, png_ptr->quantize_index);

 #endif

    if (png_ptr->free_me & PNG_FREE_PLTE)

       png_zfree(png_ptr, png_ptr->palette);

    png_ptr->free_me &= ~PNG_FREE_PLTE;

 #if defined(PNG_tRNS_SUPPORTED) || \

     defined(PNG_READ_EXPAND_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)

    if (png_ptr->free_me & PNG_FREE_TRNS)

       png_free(png_ptr, png_ptr->trans_alpha);

    png_ptr->free_me &= ~PNG_FREE_TRNS;

 #endif

    inflateEnd(&png_ptr->zstream);

 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED

    png_free(png_ptr, png_ptr->save_buffer);

 #endif

 #if defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED) &&\

    defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)

    png_free(png_ptr, png_ptr->unknown_chunk.data);

 #endif

 #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED

    png_free(png_ptr, png_ptr->chunk_list);

 #endif

    /* NOTE: the 'setjmp' buffer may still be allocated and the memory and error

     * callbacks are still set at this point.  They are required to complete the

     * destruction of the png_struct itself.

     */

 }

 /* Free all memory used by the read */

 void PNGAPI

 png_destroy_read_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr,

     png_infopp end_info_ptr_ptr)

 {

    png_structrp png_ptr = NULL;

    png_debug(1, "in png_destroy_read_struct");

    if (png_ptr_ptr != NULL)

       png_ptr = *png_ptr_ptr;

    if (png_ptr == NULL)

       return;

    /* libpng 1.6.0: use the API to destroy info structs to ensure consistent

     * behavior.  Prior to 1.6.0 libpng did extra 'info' destruction in this API.

     * The extra was, apparently, unnecessary yet this hides memory leak bugs.

     */

    png_destroy_info_struct(png_ptr, end_info_ptr_ptr);

    png_destroy_info_struct(png_ptr, info_ptr_ptr);

    *png_ptr_ptr = NULL;

    png_read_destroy(png_ptr);

    png_destroy_png_struct(png_ptr);

 }

 void PNGAPI

 png_set_read_status_fn(png_structrp png_ptr, png_read_status_ptr read_row_fn)

 {

    if (png_ptr == NULL)

       return;

    png_ptr->read_row_fn = read_row_fn;

 }

 #ifdef PNG_SEQUENTIAL_READ_SUPPORTED

 #ifdef PNG_INFO_IMAGE_SUPPORTED

 void PNGAPI

 png_read_png(png_structrp png_ptr, png_inforp info_ptr,

                            int transforms,

                            voidp params)

 {

    if (png_ptr == NULL || info_ptr == NULL)

       return;

    /* png_read_info() gives us all of the information from the

     * PNG file before the first IDAT (image data chunk).

     */

    png_read_info(png_ptr, info_ptr);

    if (info_ptr->height > PNG_UINT_32_MAX/(sizeof (png_bytep)))

       png_error(png_ptr, "Image is too high to process with png_read_png()");

    /* -------------- image transformations start here ------------------- */

    /* libpng 1.6.10: add code to cause a png_app_error if a selected TRANSFORM

     * is not implemented.  This will only happen in de-configured (non-default)

     * libpng builds.  The results can be unexpected - png_read_png may return

     * short or mal-formed rows because the transform is skipped.

     */

    /* Tell libpng to strip 16-bit/color files down to 8 bits per color.

     */

    if (transforms & PNG_TRANSFORM_SCALE_16)

      /* Added at libpng-1.5.4. "strip_16" produces the same result that it

       * did in earlier versions, while "scale_16" is now more accurate.

       */

 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED

       png_set_scale_16(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_SCALE_16 not supported");

 #endif

    /* If both SCALE and STRIP are required pngrtran will effectively cancel the

     * latter by doing SCALE first.  This is ok and allows apps not to check for

     * which is supported to get the right answer.

     */

    if (transforms & PNG_TRANSFORM_STRIP_16)

 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED

       png_set_strip_16(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_16 not supported");

 #endif

    /* Strip alpha bytes from the input data without combining with

     * the background (not recommended).

     */

    if (transforms & PNG_TRANSFORM_STRIP_ALPHA)

 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED

       png_set_strip_alpha(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_ALPHA not supported");

 #endif

    /* Extract multiple pixels with bit depths of 1, 2, or 4 from a single

     * byte into separate bytes (useful for paletted and grayscale images).

     */

    if (transforms & PNG_TRANSFORM_PACKING)

 #ifdef PNG_READ_PACK_SUPPORTED

       png_set_packing(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_PACKING not supported");

 #endif

    /* Change the order of packed pixels to least significant bit first

     * (not useful if you are using png_set_packing).

     */

    if (transforms & PNG_TRANSFORM_PACKSWAP)

 #ifdef PNG_READ_PACKSWAP_SUPPORTED

       png_set_packswap(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_PACKSWAP not supported");

 #endif

    /* Expand paletted colors into true RGB triplets

     * Expand grayscale images to full 8 bits from 1, 2, or 4 bits/pixel

     * Expand paletted or RGB images with transparency to full alpha

     * channels so the data will be available as RGBA quartets.

     */

    if (transforms & PNG_TRANSFORM_EXPAND)

 #ifdef PNG_READ_EXPAND_SUPPORTED

       png_set_expand(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND not supported");

 #endif

    /* We don't handle background color or gamma transformation or quantizing.

     */

    /* Invert monochrome files to have 0 as white and 1 as black

     */

    if (transforms & PNG_TRANSFORM_INVERT_MONO)

 #ifdef PNG_READ_INVERT_SUPPORTED

       png_set_invert_mono(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_MONO not supported");

 #endif

    /* If you want to shift the pixel values from the range [0,255] or

     * [0,65535] to the original [0,7] or [0,31], or whatever range the

     * colors were originally in:

     */

    if (transforms & PNG_TRANSFORM_SHIFT)

 #ifdef PNG_READ_SHIFT_SUPPORTED

       if (info_ptr->valid & PNG_INFO_sBIT)

          png_set_shift(png_ptr, &info_ptr->sig_bit);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_SHIFT not supported");

 #endif

    /* Flip the RGB pixels to BGR (or RGBA to BGRA) */

    if (transforms & PNG_TRANSFORM_BGR)

 #ifdef PNG_READ_BGR_SUPPORTED

       png_set_bgr(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_BGR not supported");

 #endif

    /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */

    if (transforms & PNG_TRANSFORM_SWAP_ALPHA)

 #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED

       png_set_swap_alpha(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ALPHA not supported");

 #endif

    /* Swap bytes of 16-bit files to least significant byte first */

    if (transforms & PNG_TRANSFORM_SWAP_ENDIAN)

 #ifdef PNG_READ_SWAP_SUPPORTED

       png_set_swap(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ENDIAN not supported");

 #endif

 /* Added at libpng-1.2.41 */

    /* Invert the alpha channel from opacity to transparency */

    if (transforms & PNG_TRANSFORM_INVERT_ALPHA)

 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED

       png_set_invert_alpha(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_ALPHA not supported");

 #endif

 /* Added at libpng-1.2.41 */

    /* Expand grayscale image to RGB */

    if (transforms & PNG_TRANSFORM_GRAY_TO_RGB)

 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED

       png_set_gray_to_rgb(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_GRAY_TO_RGB not supported");

 #endif

 /* Added at libpng-1.5.4 */

    if (transforms & PNG_TRANSFORM_EXPAND_16)

 #ifdef PNG_READ_EXPAND_16_SUPPORTED

       png_set_expand_16(png_ptr);

 #else

       png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND_16 not supported");

 #endif

    /* We don't handle adding filler bytes */

    /* We use png_read_image and rely on that for interlace handling, but we also

     * call png_read_update_info therefore must turn on interlace handling now:

     */

    (void)png_set_interlace_handling(png_ptr);

    /* Optional call to gamma correct and add the background to the palette

     * and update info structure.  REQUIRED if you are expecting libpng to

     * update the palette for you (i.e., you selected such a transform above).

     */

    png_read_update_info(png_ptr, info_ptr);

    /* -------------- image transformations end here ------------------- */

    png_free_data(png_ptr, info_ptr, PNG_FREE_ROWS, 0);

    if (info_ptr->row_pointers == NULL)

    {

       png_uint_32 iptr;

       info_ptr->row_pointers = png_voidcast(png_bytepp, png_malloc(png_ptr,

           info_ptr->height * (sizeof (png_bytep))));

       for (iptr=0; iptr<info_ptr->height; iptr++)

          info_ptr->row_pointers[iptr] = NULL;

       info_ptr->free_me |= PNG_FREE_ROWS;

       for (iptr = 0; iptr < info_ptr->height; iptr++)

          info_ptr->row_pointers[iptr] = png_voidcast(png_bytep,

             png_malloc(png_ptr, info_ptr->rowbytes));

    }

    png_read_image(png_ptr, info_ptr->row_pointers);

    info_ptr->valid |= PNG_INFO_IDAT;

    /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */

    png_read_end(png_ptr, info_ptr);

    PNG_UNUSED(params)

 }

 #endif /* PNG_INFO_IMAGE_SUPPORTED */

 #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

 #ifdef PNG_SIMPLIFIED_READ_SUPPORTED

 /* SIMPLIFIED READ

  *

  * This code currently relies on the sequential reader, though it could easily

  * be made to work with the progressive one.

  */

 /* Arguments to png_image_finish_read: */

 /* Encoding of PNG data (used by the color-map code) */

 #  define P_NOTSET  0 /* File encoding not yet known */

 #  define P_sRGB    1 /* 8-bit encoded to sRGB gamma */

 #  define P_LINEAR  2 /* 16-bit linear: not encoded, NOT pre-multiplied! */

 #  define P_FILE    3 /* 8-bit encoded to file gamma, not sRGB or linear */

 #  define P_LINEAR8 4 /* 8-bit linear: only from a file value */

 /* Color-map processing: after libpng has run on the PNG image further

  * processing may be needed to conver the data to color-map indicies.

  */

 #define PNG_CMAP_NONE      0

 #define PNG_CMAP_GA        1 /* Process GA data to a color-map with alpha */

 #define PNG_CMAP_TRANS     2 /* Process GA data to a background index */

 #define PNG_CMAP_RGB       3 /* Process RGB data */

 #define PNG_CMAP_RGB_ALPHA 4 /* Process RGBA data */

 /* The following document where the background is for each processing case. */

 #define PNG_CMAP_NONE_BACKGROUND      256

 #define PNG_CMAP_GA_BACKGROUND        231

 #define PNG_CMAP_TRANS_BACKGROUND     254

 #define PNG_CMAP_RGB_BACKGROUND       256

 #define PNG_CMAP_RGB_ALPHA_BACKGROUND 216

 typedef struct

 {

    /* Arguments: */

    png_imagep image;

    png_voidp  buffer;

    png_int_32 row_stride;

    png_voidp  colormap;

    png_const_colorp background;

    /* Local variables: */

    png_voidp       local_row;

    png_voidp       first_row;

    ptrdiff_t       row_bytes;           /* step between rows */

    int             file_encoding;       /* E_ values above */

    png_fixed_point gamma_to_linear;     /* For P_FILE, reciprocal of gamma */

    int             colormap_processing; /* PNG_CMAP_ values above */

 } png_image_read_control;

 /* Do all the *safe* initialization - 'safe' means that png_error won't be

  * called, so setting up the jmp_buf is not required.  This means that anything

  * called from here must *not* call png_malloc - it has to call png_malloc_warn

  * instead so that control is returned safely back to this routine.

  */

 static int

 png_image_read_init(png_imagep image)

 {

    if (image->opaque == NULL)

    {

       png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, image,

           png_safe_error, png_safe_warning);

       /* And set the rest of the structure to NULL to ensure that the various

        * fields are consistent.

        */

       memset(image, 0, (sizeof *image));

       image->version = PNG_IMAGE_VERSION;

       if (png_ptr != NULL)

       {

          png_infop info_ptr = png_create_info_struct(png_ptr);

          if (info_ptr != NULL)

          {

             png_controlp control = png_voidcast(png_controlp,

                png_malloc_warn(png_ptr, (sizeof *control)));

             if (control != NULL)

             {

                memset(control, 0, (sizeof *control));

                control->png_ptr = png_ptr;

                control->info_ptr = info_ptr;

                control->for_write = 0;

                image->opaque = control;

                return 1;

             }

             /* Error clean up */

             png_destroy_info_struct(png_ptr, &info_ptr);

          }

          png_destroy_read_struct(&png_ptr, NULL, NULL);

       }

       return png_image_error(image, "png_image_read: out of memory");

    }

    return png_image_error(image, "png_image_read: opaque pointer not NULL");

 }

 /* Utility to find the base format of a PNG file from a png_struct. */

 static png_uint_32

 png_image_format(png_structrp png_ptr)

 {

    png_uint_32 format = 0;

    if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)

       format |= PNG_FORMAT_FLAG_COLOR;

    if (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)

       format |= PNG_FORMAT_FLAG_ALPHA;

    /* Use png_ptr here, not info_ptr, because by examination png_handle_tRNS

     * sets the png_struct fields; that's all we are interested in here.  The

     * precise interaction with an app call to png_set_tRNS and PNG file reading

     * is unclear.

     */

    else if (png_ptr->num_trans > 0)

       format |= PNG_FORMAT_FLAG_ALPHA;

    if (png_ptr->bit_depth == 16)

       format |= PNG_FORMAT_FLAG_LINEAR;

    if (png_ptr->color_type & PNG_COLOR_MASK_PALETTE)

       format |= PNG_FORMAT_FLAG_COLORMAP;

    return format;

 }

 /* Is the given gamma significantly different from sRGB?  The test is the same

  * one used in pngrtran.c when deciding whether to do gamma correction.  The

  * arithmetic optimizes the division by using the fact that the inverse of the

  * file sRGB gamma is 2.2

  */

 static int

 png_gamma_not_sRGB(png_fixed_point g)

 {

    if (g < PNG_FP_1)

    {

       /* An uninitialized gamma is assumed to be sRGB for the simplified API. */

       if (g == 0)

          return 0;

       return png_gamma_significant((g * 11 + 2)/5 /* i.e. *2.2, rounded */);

    }

    return 1;

 }

 /* Do the main body of a 'png_image_begin_read' function; read the PNG file

  * header and fill in all the information.  This is executed in a safe context,

  * unlike the init routine above.

  */

 static int

 png_image_read_header(png_voidp argument)

 {

    png_imagep image = png_voidcast(png_imagep, argument);

    png_structrp png_ptr = image->opaque->png_ptr;

    png_inforp info_ptr = image->opaque->info_ptr;

    png_set_benign_errors(png_ptr, 1/*warn*/);

    png_read_info(png_ptr, info_ptr);

    /* Do this the fast way; just read directly out of png_struct. */

    image->width = png_ptr->width;

    image->height = png_ptr->height;

    {

       png_uint_32 format = png_image_format(png_ptr);

       image->format = format;

 #ifdef PNG_COLORSPACE_SUPPORTED

       /* Does the colorspace match sRGB?  If there is no color endpoint

        * (colorant) information assume yes, otherwise require the

        * 'ENDPOINTS_MATCHP_sRGB' colorspace flag to have been set.  If the

        * colorspace has been determined to be invalid ignore it.

        */

       if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags

          & (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB|

             PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))

          image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;

 #endif

    }

    /* We need the maximum number of entries regardless of the format the

     * application sets here.

     */

    {

       png_uint_32 cmap_entries;

       switch (png_ptr->color_type)

       {

          case PNG_COLOR_TYPE_GRAY:

             cmap_entries = 1U << png_ptr->bit_depth;

             break;

          case PNG_COLOR_TYPE_PALETTE:

             cmap_entries = png_ptr->num_palette;

             break;

          default:

             cmap_entries = 256;

             break;

       }

       if (cmap_entries > 256)

          cmap_entries = 256;

       image->colormap_entries = cmap_entries;

    }

    return 1;

 }

 #ifdef PNG_STDIO_SUPPORTED

 int PNGAPI

 png_image_begin_read_from_stdio(png_imagep image, FILE* file)

 {

    if (image != NULL && image->version == PNG_IMAGE_VERSION)

    {

       if (file != NULL)

       {

          if (png_image_read_init(image))

          {

             /* This is slightly evil, but png_init_io doesn't do anything other

              * than this and we haven't changed the standard IO functions so

              * this saves a 'safe' function.

              */

             image->opaque->png_ptr->io_ptr = file;

             return png_safe_execute(image, png_image_read_header, image);

          }

       }

       else

          return png_image_error(image,

             "png_image_begin_read_from_stdio: invalid argument");

    }

    else if (image != NULL)

       return png_image_error(image,

          "png_image_begin_read_from_stdio: incorrect PNG_IMAGE_VERSION");

    return 0;

 }

 int PNGAPI

 png_image_begin_read_from_file(png_imagep image, const char *file_name)

 {

    if (image != NULL && image->version == PNG_IMAGE_VERSION)

    {

       if (file_name != NULL)

       {

          FILE *fp = fopen(file_name, "rb");

          if (fp != NULL)

          {

             if (png_image_read_init(image))

             {

                image->opaque->png_ptr->io_ptr = fp;

                image->opaque->owned_file = 1;

                return png_safe_execute(image, png_image_read_header, image);

             }

             /* Clean up: just the opened file. */

             (void)fclose(fp);

          }

          else

             return png_image_error(image, strerror(errno));

       }

       else

          return png_image_error(image,

             "png_image_begin_read_from_file: invalid argument");

    }

    else if (image != NULL)

       return png_image_error(image,

          "png_image_begin_read_from_file: incorrect PNG_IMAGE_VERSION");

    return 0;

 }

 #endif /* PNG_STDIO_SUPPORTED */

 static void PNGCBAPI

 png_image_memory_read(png_structp png_ptr, png_bytep out, png_size_t need)

 {

    if (png_ptr != NULL)

    {

       png_imagep image = png_voidcast(png_imagep, png_ptr->io_ptr);

       if (image != NULL)

       {

          png_controlp cp = image->opaque;

          if (cp != NULL)

          {

             png_const_bytep memory = cp->memory;

             png_size_t size = cp->size;

             if (memory != NULL && size >= need)

             {

                memcpy(out, memory, need);

                cp->memory = memory + need;

                cp->size = size - need;

                return;

             }

             png_error(png_ptr, "read beyond end of data");

          }

       }

       png_error(png_ptr, "invalid memory read");

    }

 }

 int PNGAPI png_image_begin_read_from_memory(png_imagep image,

    png_const_voidp memory, png_size_t size)

 {

    if (image != NULL && image->version == PNG_IMAGE_VERSION)

    {

       if (memory != NULL && size > 0)

       {

          if (png_image_read_init(image))

          {

             /* Now set the IO functions to read from the memory buffer and

              * store it into io_ptr.  Again do this in-place to avoid calling a

              * libpng function that requires error handling.

              */

             image->opaque->memory = png_voidcast(png_const_bytep, memory);

             image->opaque->size = size;

             image->opaque->png_ptr->io_ptr = image;

             image->opaque->png_ptr->read_data_fn = png_image_memory_read;

             return png_safe_execute(image, png_image_read_header, image);

          }

       }

       else

          return png_image_error(image,

             "png_image_begin_read_from_memory: invalid argument");

    }

    else if (image != NULL)

       return png_image_error(image,

          "png_image_begin_read_from_memory: incorrect PNG_IMAGE_VERSION");

    return 0;

 }

 /* Utility function to skip chunks that are not used by the simplified image

  * read functions and an appropriate macro to call it.

  */

 #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

 static void

 png_image_skip_unused_chunks(png_structrp png_ptr)

 {

    /* Prepare the reader to ignore all recognized chunks whose data will not

     * be used, i.e., all chunks recognized by libpng except for those

     * involved in basic image reading:

     *

     *    IHDR, PLTE, IDAT, IEND

     *

     * Or image data handling:

     *

     *    tRNS, bKGD, gAMA, cHRM, sRGB, [iCCP] and sBIT.

     *

     * This provides a small performance improvement and eliminates any

     * potential vulnerability to security problems in the unused chunks.

     *

     * At present the iCCP chunk data isn't used, so iCCP chunk can be ignored

     * too.  This allows the simplified API to be compiled without iCCP support,

     * however if the support is there the chunk is still checked to detect

     * errors (which are unfortunately quite common.)

     */

    {

          static PNG_CONST png_byte chunks_to_process[] = {

             98,  75,  71,  68, '\0',  /* bKGD */

             99,  72,  82,  77, '\0',  /* cHRM */

            103,  65,  77,  65, '\0',  /* gAMA */

 #        ifdef PNG_READ_iCCP_SUPPORTED

            105,  67,  67,  80, '\0',  /* iCCP */

 #        endif

            115,  66,  73,  84, '\0',  /* sBIT */

            115,  82,  71,  66, '\0',  /* sRGB */

            };

        /* Ignore unknown chunks and all other chunks except for the

         * IHDR, PLTE, tRNS, IDAT, and IEND chunks.

         */

        png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_NEVER,

          NULL, -1);

        /* But do not ignore image data handling chunks */

        png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_AS_DEFAULT,

          chunks_to_process, (sizeof chunks_to_process)/5);

     }

 }

 #  define PNG_SKIP_CHUNKS(p) png_image_skip_unused_chunks(p)

 #else

 #  define PNG_SKIP_CHUNKS(p) ((void)0)

 #endif /* PNG_HANDLE_AS_UNKNOWN_SUPPORTED */

 /* The following macro gives the exact rounded answer for all values in the

  * range 0..255 (it actually divides by 51.2, but the rounding still generates

  * the correct numbers 0..5

  */

 #define PNG_DIV51(v8) (((v8) * 5 + 130) >> 8)

 /* Utility functions to make particular color-maps */

 static void

 set_file_encoding(png_image_read_control *display)

 {

    png_fixed_point g = display->image->opaque->png_ptr->colorspace.gamma;

    if (png_gamma_significant(g))

    {

       if (png_gamma_not_sRGB(g))

       {

          display->file_encoding = P_FILE;

          display->gamma_to_linear = png_reciprocal(g);

       }

       else

          display->file_encoding = P_sRGB;

    }

    else

       display->file_encoding = P_LINEAR8;

 }

 static unsigned int

 decode_gamma(png_image_read_control *display, png_uint_32 value, int encoding)

 {

    if (encoding == P_FILE) /* double check */

       encoding = display->file_encoding;

    if (encoding == P_NOTSET) /* must be the file encoding */

    {

       set_file_encoding(display);

       encoding = display->file_encoding;

    }

    switch (encoding)

    {

       case P_FILE:

          value = png_gamma_16bit_correct(value*257, display->gamma_to_linear);

          break;

       case P_sRGB:

          value = png_sRGB_table[value];

          break;

       case P_LINEAR:

          break;

       case P_LINEAR8:

          value *= 257;

          break;

       default:

          png_error(display->image->opaque->png_ptr,

             "unexpected encoding (internal error)");

          break;

    }

    return value;

 }

 static png_uint_32

 png_colormap_compose(png_image_read_control *display,

    png_uint_32 foreground, int foreground_encoding, png_uint_32 alpha,

    png_uint_32 background, int encoding)

 {

    /* The file value is composed on the background, the background has the given

     * encoding and so does the result, the file is encoded with P_FILE and the

     * file and alpha are 8-bit values.  The (output) encoding will always be

     * P_LINEAR or P_sRGB.

     */

    png_uint_32 f = decode_gamma(display, foreground, foreground_encoding);

    png_uint_32 b = decode_gamma(display, background, encoding);

    /* The alpha is always an 8-bit value (it comes from the palette), the value

     * scaled by 255 is what PNG_sRGB_FROM_LINEAR requires.

     */

    f = f * alpha + b * (255-alpha);

    if (encoding == P_LINEAR)

    {

       /* Scale to 65535; divide by 255, approximately (in fact this is extremely

        * accurate, it divides by 255.00000005937181414556, with no overflow.)

        */

       f *= 257; /* Now scaled by 65535 */

       f += f >> 16;

       f = (f+32768) >> 16;

    }

    else /* P_sRGB */

       f = PNG_sRGB_FROM_LINEAR(f);

    return f;

 }

 /* NOTE: P_LINEAR values to this routine must be 16-bit, but P_FILE values must

  * be 8-bit.

  */

 static void

 png_create_colormap_entry(png_image_read_control *display,

    png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,

    png_uint_32 alpha, int encoding)

 {

    png_imagep image = display->image;

    const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) ?

       P_LINEAR : P_sRGB;

    const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&

       (red != green || green != blue);

    if (ip > 255)

       png_error(image->opaque->png_ptr, "color-map index out of range");

    /* Update the cache with whether the file gamma is significantly different

     * from sRGB.

     */

    if (encoding == P_FILE)

    {

       if (display->file_encoding == P_NOTSET)

          set_file_encoding(display);

       /* Note that the cached value may be P_FILE too, but if it is then the

        * gamma_to_linear member has been set.

        */

       encoding = display->file_encoding;

    }

    if (encoding == P_FILE)

    {

       png_fixed_point g = display->gamma_to_linear;

       red = png_gamma_16bit_correct(red*257, g);

       green = png_gamma_16bit_correct(green*257, g);

       blue = png_gamma_16bit_correct(blue*257, g);

       if (convert_to_Y || output_encoding == P_LINEAR)

       {

          alpha *= 257;

          encoding = P_LINEAR;

       }

       else

       {

          red = PNG_sRGB_FROM_LINEAR(red * 255);

          green = PNG_sRGB_FROM_LINEAR(green * 255);

          blue = PNG_sRGB_FROM_LINEAR(blue * 255);

          encoding = P_sRGB;

       }

    }

    else if (encoding == P_LINEAR8)

    {

       /* This encoding occurs quite frequently in test cases because PngSuite

        * includes a gAMA 1.0 chunk with most images.

        */

       red *= 257;

       green *= 257;

       blue *= 257;

       alpha *= 257;

       encoding = P_LINEAR;

    }

    else if (encoding == P_sRGB && (convert_to_Y || output_encoding == P_LINEAR))

    {

       /* The values are 8-bit sRGB values, but must be converted to 16-bit

        * linear.

        */

       red = png_sRGB_table[red];

       green = png_sRGB_table[green];

       blue = png_sRGB_table[blue];

       alpha *= 257;

       encoding = P_LINEAR;

    }

    /* This is set if the color isn't gray but the output is. */

    if (encoding == P_LINEAR)

    {

       if (convert_to_Y)

       {

          /* NOTE: these values are copied from png_do_rgb_to_gray */

          png_uint_32 y = (png_uint_32)6968 * red  + (png_uint_32)23434 * green +

             (png_uint_32)2366 * blue;

          if (output_encoding == P_LINEAR)

             y = (y + 16384) >> 15;

          else

          {

             /* y is scaled by 32768, we need it scaled by 255: */

             y = (y + 128) >> 8;

             y *= 255;

             y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);

             encoding = P_sRGB;

          }

          blue = red = green = y;

       }

       else if (output_encoding == P_sRGB)

       {

          red = PNG_sRGB_FROM_LINEAR(red * 255);

          green = PNG_sRGB_FROM_LINEAR(green * 255);

          blue = PNG_sRGB_FROM_LINEAR(blue * 255);

          alpha = PNG_DIV257(alpha);

          encoding = P_sRGB;

       }

    }

    if (encoding != output_encoding)

       png_error(image->opaque->png_ptr, "bad encoding (internal error)");

    /* Store the value. */

    {

 #     ifdef PNG_FORMAT_AFIRST_SUPPORTED

          const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&

             (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;

 #     else

 #        define afirst 0

 #     endif

 #     ifdef PNG_FORMAT_BGR_SUPPORTED

          const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) ? 2 : 0;

 #     else

 #        define bgr 0

 #     endif

       if (output_encoding == P_LINEAR)

       {

          png_uint_16p entry = png_voidcast(png_uint_16p, display->colormap);

          entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

          /* The linear 16-bit values must be pre-multiplied by the alpha channel

           * value, if less than 65535 (this is, effectively, composite on black

           * if the alpha channel is removed.)

           */

          switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))

          {

             case 4:

                entry[afirst ? 0 : 3] = (png_uint_16)alpha;

                /* FALL THROUGH */

             case 3:

                if (alpha < 65535)

                {

                   if (alpha > 0)

                   {

                      blue = (blue * alpha + 32767U)/65535U;

                      green = (green * alpha + 32767U)/65535U;

                      red = (red * alpha + 32767U)/65535U;

                   }

                   else

                      red = green = blue = 0;

                }

                entry[afirst + (2 ^ bgr)] = (png_uint_16)blue;

                entry[afirst + 1] = (png_uint_16)green;

                entry[afirst + bgr] = (png_uint_16)red;

                break;

             case 2:

                entry[1 ^ afirst] = (png_uint_16)alpha;

                /* FALL THROUGH */

             case 1:

                if (alpha < 65535)

                {

                   if (alpha > 0)

                      green = (green * alpha + 32767U)/65535U;

                   else

                      green = 0;

                }

                entry[afirst] = (png_uint_16)green;

                break;

             default:

                break;

          }

       }

       else /* output encoding is P_sRGB */

       {

          png_bytep entry = png_voidcast(png_bytep, display->colormap);

          entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

          switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))

          {

             case 4:

                entry[afirst ? 0 : 3] = (png_byte)alpha;

             case 3:

                entry[afirst + (2 ^ bgr)] = (png_byte)blue;

                entry[afirst + 1] = (png_byte)green;

                entry[afirst + bgr] = (png_byte)red;

                break;

             case 2:

                entry[1 ^ afirst] = (png_byte)alpha;

             case 1:

                entry[afirst] = (png_byte)green;

                break;

             default:

                break;

          }

       }

 #     ifdef afirst

 #        undef afirst

 #     endif

 #     ifdef bgr

 #        undef bgr

 #     endif

    }

 }

 static int

 make_gray_file_colormap(png_image_read_control *display)

 {

    unsigned int i;

    for (i=0; i<256; ++i)

       png_create_colormap_entry(display, i, i, i, i, 255, P_FILE);

    return i;

 }

 static int

 make_gray_colormap(png_image_read_control *display)

 {

    unsigned int i;

    for (i=0; i<256; ++i)

       png_create_colormap_entry(display, i, i, i, i, 255, P_sRGB);

    return i;

 }

 #define PNG_GRAY_COLORMAP_ENTRIES 256

 static int

 make_ga_colormap(png_image_read_control *display)

 {

    unsigned int i, a;

    /* Alpha is retained, the output will be a color-map with entries

     * selected by six levels of alpha.  One transparent entry, 6 gray

     * levels for all the intermediate alpha values, leaving 230 entries

     * for the opaque grays.  The color-map entries are the six values

     * [0..5]*51, the GA processing uses PNG_DIV51(value) to find the

     * relevant entry.

     *

     * if (alpha > 229) // opaque

     * {

     *    // The 231 entries are selected to make the math below work:

     *    base = 0;

     *    entry = (231 * gray + 128) >> 8;

     * }

     * else if (alpha < 26) // transparent

     * {

     *    base = 231;

     *    entry = 0;

     * }

     * else // partially opaque

     * {

     *    base = 226 + 6 * PNG_DIV51(alpha);

     *    entry = PNG_DIV51(gray);

     * }

     */

    i = 0;

    while (i < 231)

    {

       unsigned int gray = (i * 256 + 115) / 231;

       png_create_colormap_entry(display, i++, gray, gray, gray, 255, P_sRGB);

    }

    /* 255 is used here for the component values for consistency with the code

     * that undoes premultiplication in pngwrite.c.

     */

    png_create_colormap_entry(display, i++, 255, 255, 255, 0, P_sRGB);

    for (a=1; a<5; ++a)

    {

       unsigned int g;

       for (g=0; g<6; ++g)

          png_create_colormap_entry(display, i++, g*51, g*51, g*51, a*51,

             P_sRGB);

    }

    return i;

 }

 #define PNG_GA_COLORMAP_ENTRIES 256

 static int

 make_rgb_colormap(png_image_read_control *display)

 {

    unsigned int i, r;

    /* Build a 6x6x6 opaque RGB cube */

    for (i=r=0; r<6; ++r)

    {

       unsigned int g;

       for (g=0; g<6; ++g)

       {

          unsigned int b;

          for (b=0; b<6; ++b)

             png_create_colormap_entry(display, i++, r*51, g*51, b*51, 255,

                P_sRGB);

       }

    }

    return i;

 }

 #define PNG_RGB_COLORMAP_ENTRIES 216

 /* Return a palette index to the above palette given three 8-bit sRGB values. */

 #define PNG_RGB_INDEX(r,g,b) \

    ((png_byte)(6 * (6 * PNG_DIV51(r) + PNG_DIV51(g)) + PNG_DIV51(b)))

 static int

 png_image_read_colormap(png_voidp argument)

 {

    png_image_read_control *display =

       png_voidcast(png_image_read_control*, argument);

    const png_imagep image = display->image;

    const png_structrp png_ptr = image->opaque->png_ptr;

    const png_uint_32 output_format = image->format;

    const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) ?

       P_LINEAR : P_sRGB;

    unsigned int cmap_entries;

    unsigned int output_processing;        /* Output processing option */

    unsigned int data_encoding = P_NOTSET; /* Encoding libpng must produce */

    /* Background information; the background color and the index of this color

     * in the color-map if it exists (else 256).

     */

    unsigned int background_index = 256;

    png_uint_32 back_r, back_g, back_b;

    /* Flags to accumulate things that need to be done to the input. */

    int expand_tRNS = 0;

    /* Exclude the NYI feature of compositing onto a color-mapped buffer; it is

     * very difficult to do, the results look awful, and it is difficult to see

     * what possible use it is because the application can't control the

     * color-map.

     */

    if (((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0 ||

          png_ptr->num_trans > 0) /* alpha in input */ &&

       ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0) /* no alpha in output */)

    {

       if (output_encoding == P_LINEAR) /* compose on black */

          back_b = back_g = back_r = 0;

       else if (display->background == NULL /* no way to remove it */)

          png_error(png_ptr,

             "a background color must be supplied to remove alpha/transparency");

       /* Get a copy of the background color (this avoids repeating the checks

        * below.)  The encoding is 8-bit sRGB or 16-bit linear, depending on the

        * output format.

        */

       else

       {

          back_g = display->background->green;

          if (output_format & PNG_FORMAT_FLAG_COLOR)

          {

             back_r = display->background->red;

             back_b = display->background->blue;

          }

          else

             back_b = back_r = back_g;

       }

    }

    else if (output_encoding == P_LINEAR)

       back_b = back_r = back_g = 65535;

    else

       back_b = back_r = back_g = 255;

    /* Default the input file gamma if required - this is necessary because

     * libpng assumes that if no gamma information is present the data is in the

     * output format, but the simplified API deduces the gamma from the input

     * format.

     */

    if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) == 0)

    {

       /* Do this directly, not using the png_colorspace functions, to ensure

        * that it happens even if the colorspace is invalid (though probably if

        * it is the setting will be ignored)  Note that the same thing can be

        * achieved at the application interface with png_set_gAMA.

        */

       if (png_ptr->bit_depth == 16 &&

          (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)

          png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;

       else

          png_ptr->colorspace.gamma = PNG_GAMMA_sRGB_INVERSE;

       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;

    }

    /* Decide what to do based on the PNG color type of the input data.  The

     * utility function png_create_colormap_entry deals with most aspects of the

     * output transformations; this code works out how to produce bytes of

     * color-map entries from the original format.

     */

    switch (png_ptr->color_type)

    {

       case PNG_COLOR_TYPE_GRAY:

          if (png_ptr->bit_depth <= 8)

          {

             /* There at most 256 colors in the output, regardless of

              * transparency.

              */

             unsigned int step, i, val, trans = 256/*ignore*/, back_alpha = 0;

             cmap_entries = 1U << png_ptr->bit_depth;

             if (cmap_entries > image->colormap_entries)

                png_error(png_ptr, "gray[8] color-map: too few entries");

             step = 255 / (cmap_entries - 1);

             output_processing = PNG_CMAP_NONE;

             /* If there is a tRNS chunk then this either selects a transparent

              * value or, if the output has no alpha, the background color.

              */

             if (png_ptr->num_trans > 0)

             {

                trans = png_ptr->trans_color.gray;

                if ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0)

                   back_alpha = output_encoding == P_LINEAR ? 65535 : 255;

             }

             /* png_create_colormap_entry just takes an RGBA and writes the

              * corresponding color-map entry using the format from 'image',

              * including the required conversion to sRGB or linear as

              * appropriate.  The input values are always either sRGB (if the

              * gamma correction flag is 0) or 0..255 scaled file encoded values

              * (if the function must gamma correct them).

              */

             for (i=val=0; i<cmap_entries; ++i, val += step)

             {

                /* 'i' is a file value.  While this will result in duplicated

                 * entries for 8-bit non-sRGB encoded files it is necessary to

                 * have non-gamma corrected values to do tRNS handling.

                 */

                if (i != trans)

                   png_create_colormap_entry(display, i, val, val, val, 255,

                      P_FILE/*8-bit with file gamma*/);

                /* Else this entry is transparent.  The colors don't matter if

                 * there is an alpha channel (back_alpha == 0), but it does no

                 * harm to pass them in; the values are not set above so this

                 * passes in white.

                 *

                 * NOTE: this preserves the full precision of the application

                 * supplied background color when it is used.

                 */

                else

                   png_create_colormap_entry(display, i, back_r, back_g, back_b,

                      back_alpha, output_encoding);

             }

             /* We need libpng to preserve the original encoding. */

             data_encoding = P_FILE;

             /* The rows from libpng, while technically gray values, are now also

              * color-map indicies; however, they may need to be expanded to 1

              * byte per pixel.  This is what png_set_packing does (i.e., it

              * unpacks the bit values into bytes.)

              */

             if (png_ptr->bit_depth < 8)

                png_set_packing(png_ptr);

          }

          else /* bit depth is 16 */

          {

             /* The 16-bit input values can be converted directly to 8-bit gamma

              * encoded values; however, if a tRNS chunk is present 257 color-map

              * entries are required.  This means that the extra entry requires

              * special processing; add an alpha channel, sacrifice gray level

              * 254 and convert transparent (alpha==0) entries to that.

              *

              * Use libpng to chop the data to 8 bits.  Convert it to sRGB at the

              * same time to minimize quality loss.  If a tRNS chunk is present

              * this means libpng must handle it too; otherwise it is impossible

              * to do the exact match on the 16-bit value.

              *

              * If the output has no alpha channel *and* the background color is

              * gray then it is possible to let libpng handle the substitution by

              * ensuring that the corresponding gray level matches the background

              * color exactly.

              */

             data_encoding = P_sRGB;

             if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)

                png_error(png_ptr, "gray[16] color-map: too few entries");

             cmap_entries = make_gray_colormap(display);

             if (png_ptr->num_trans > 0)

             {

                unsigned int back_alpha;

                if (output_format & PNG_FORMAT_FLAG_ALPHA)

                   back_alpha = 0;

                else

                {

                   if (back_r == back_g && back_g == back_b)

                   {

                      /* Background is gray; no special processing will be

                       * required.

                       */

                      png_color_16 c;

                      png_uint_32 gray = back_g;

                      if (output_encoding == P_LINEAR)

                      {

                         gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                         /* And make sure the corresponding palette entry

                          * matches.

                          */

                         png_create_colormap_entry(display, gray, back_g, back_g,

                            back_g, 65535, P_LINEAR);

                      }

                      /* The background passed to libpng, however, must be the

                       * sRGB value.

                       */

                      c.index = 0; /*unused*/

                      c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                      /* NOTE: does this work without expanding tRNS to alpha?

                       * It should be the color->gray case below apparently

                       * doesn't.

                       */

                      png_set_background_fixed(png_ptr, &c,

                         PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,

                         0/*gamma: not used*/);

                      output_processing = PNG_CMAP_NONE;

                      break;

                   }

                   back_alpha = output_encoding == P_LINEAR ? 65535 : 255;

                }

                /* output_processing means that the libpng-processed row will be

                 * 8-bit GA and it has to be processing to single byte color-map

                 * values.  Entry 254 is replaced by either a completely

                 * transparent entry or by the background color at full

                 * precision (and the background color is not a simple gray leve

                 * in this case.)

                 */

                expand_tRNS = 1;

                output_processing = PNG_CMAP_TRANS;

                background_index = 254;

                /* And set (overwrite) color-map entry 254 to the actual

                 * background color at full precision.

                 */

                png_create_colormap_entry(display, 254, back_r, back_g, back_b,

                   back_alpha, output_encoding);

             }

             else

                output_processing = PNG_CMAP_NONE;

          }

          break;

       case PNG_COLOR_TYPE_GRAY_ALPHA:

          /* 8-bit or 16-bit PNG with two channels - gray and alpha.  A minimum

           * of 65536 combinations.  If, however, the alpha channel is to be

           * removed there are only 256 possibilities if the background is gray.

           * (Otherwise there is a subset of the 65536 possibilities defined by

           * the triangle between black, white and the background color.)

           *

           * Reduce 16-bit files to 8-bit and sRGB encode the result.  No need to

           * worry about tRNS matching - tRNS is ignored if there is an alpha

           * channel.

           */

          data_encoding = P_sRGB;

          if (output_format & PNG_FORMAT_FLAG_ALPHA)

          {

             if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)

                png_error(png_ptr, "gray+alpha color-map: too few entries");

             cmap_entries = make_ga_colormap(display);

             background_index = PNG_CMAP_GA_BACKGROUND;

             output_processing = PNG_CMAP_GA;

          }

          else /* alpha is removed */

          {

             /* Alpha must be removed as the PNG data is processed when the

              * background is a color because the G and A channels are

              * independent and the vector addition (non-parallel vectors) is a

              * 2-D problem.

              *

              * This can be reduced to the same algorithm as above by making a

              * colormap containing gray levels (for the opaque grays), a

              * background entry (for a transparent pixel) and a set of four six

              * level color values, one set for each intermediate alpha value.

              * See the comments in make_ga_colormap for how this works in the

              * per-pixel processing.

              *

              * If the background is gray, however, we only need a 256 entry gray

              * level color map.  It is sufficient to make the entry generated

              * for the background color be exactly the color specified.

              */

             if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0 ||

                (back_r == back_g && back_g == back_b))

             {

                /* Background is gray; no special processing will be required. */

                png_color_16 c;

                png_uint_32 gray = back_g;

                if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)

                   png_error(png_ptr, "gray-alpha color-map: too few entries");

                cmap_entries = make_gray_colormap(display);

                if (output_encoding == P_LINEAR)

                {

                   gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                   /* And make sure the corresponding palette entry matches. */

                   png_create_colormap_entry(display, gray, back_g, back_g,

                      back_g, 65535, P_LINEAR);

                }

                /* The background passed to libpng, however, must be the sRGB

                 * value.

                 */

                c.index = 0; /*unused*/

                c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                png_set_background_fixed(png_ptr, &c,

                   PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,

                   0/*gamma: not used*/);

                output_processing = PNG_CMAP_NONE;

             }

             else

             {

                png_uint_32 i, a;

                /* This is the same as png_make_ga_colormap, above, except that

                 * the entries are all opaque.

                 */

                if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)

                   png_error(png_ptr, "ga-alpha color-map: too few entries");

                i = 0;

                while (i < 231)

                {

                   png_uint_32 gray = (i * 256 + 115) / 231;

                   png_create_colormap_entry(display, i++, gray, gray, gray,

                      255, P_sRGB);

                }

                /* NOTE: this preserves the full precision of the application

                 * background color.

                 */

                background_index = i;

                png_create_colormap_entry(display, i++, back_r, back_g, back_b,

                   output_encoding == P_LINEAR ? 65535U : 255U, output_encoding);

                /* For non-opaque input composite on the sRGB background - this

                 * requires inverting the encoding for each component.  The input

                 * is still converted to the sRGB encoding because this is a

                 * reasonable approximate to the logarithmic curve of human

                 * visual sensitivity, at least over the narrow range which PNG

                 * represents.  Consequently 'G' is always sRGB encoded, while

                 * 'A' is linear.  We need the linear background colors.

                 */

                if (output_encoding == P_sRGB) /* else already linear */

                {

                   /* This may produce a value not exactly matching the

                    * background, but that's ok because these numbers are only

                    * used when alpha != 0

                    */

                   back_r = png_sRGB_table[back_r];

                   back_g = png_sRGB_table[back_g];

                   back_b = png_sRGB_table[back_b];

                }

                for (a=1; a<5; ++a)

                {

                   unsigned int g;

                   /* PNG_sRGB_FROM_LINEAR expects a 16-bit linear value scaled

                    * by an 8-bit alpha value (0..255).

                    */

                   png_uint_32 alpha = 51 * a;

                   png_uint_32 back_rx = (255-alpha) * back_r;

                   png_uint_32 back_gx = (255-alpha) * back_g;

                   png_uint_32 back_bx = (255-alpha) * back_b;

                   for (g=0; g<6; ++g)

                   {

                      png_uint_32 gray = png_sRGB_table[g*51] * alpha;

                      png_create_colormap_entry(display, i++,

                         PNG_sRGB_FROM_LINEAR(gray + back_rx),

                         PNG_sRGB_FROM_LINEAR(gray + back_gx),

                         PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, P_sRGB);

                   }

                }

                cmap_entries = i;

                output_processing = PNG_CMAP_GA;

             }

          }

          break;

       case PNG_COLOR_TYPE_RGB:

       case PNG_COLOR_TYPE_RGB_ALPHA:

          /* Exclude the case where the output is gray; we can always handle this

           * with the cases above.

           */

          if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0)

          {

             /* The color-map will be grayscale, so we may as well convert the

              * input RGB values to a simple grayscale and use the grayscale

              * code above.

              *

              * NOTE: calling this apparently damages the recognition of the

              * transparent color in background color handling; call

              * png_set_tRNS_to_alpha before png_set_background_fixed.

              */

             png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE, -1,

                -1);

             data_encoding = P_sRGB;

             /* The output will now be one or two 8-bit gray or gray+alpha

              * channels.  The more complex case arises when the input has alpha.

              */

             if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||

                png_ptr->num_trans > 0) &&

                (output_format & PNG_FORMAT_FLAG_ALPHA) != 0)

             {

                /* Both input and output have an alpha channel, so no background

                 * processing is required; just map the GA bytes to the right

                 * color-map entry.

                 */

                expand_tRNS = 1;

                if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)

                   png_error(png_ptr, "rgb[ga] color-map: too few entries");

                cmap_entries = make_ga_colormap(display);

                background_index = PNG_CMAP_GA_BACKGROUND;

                output_processing = PNG_CMAP_GA;

             }

             else

             {

                /* Either the input or the output has no alpha channel, so there

                 * will be no non-opaque pixels in the color-map; it will just be

                 * grayscale.

                 */

                if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)

                   png_error(png_ptr, "rgb[gray] color-map: too few entries");

                /* Ideally this code would use libpng to do the gamma correction,

                 * but if an input alpha channel is to be removed we will hit the

                 * libpng bug in gamma+compose+rgb-to-gray (the double gamma

                 * correction bug).  Fix this by dropping the gamma correction in

                 * this case and doing it in the palette; this will result in

                 * duplicate palette entries, but that's better than the

                 * alternative of double gamma correction.

                 */

                if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||

                   png_ptr->num_trans > 0) &&

                   png_gamma_not_sRGB(png_ptr->colorspace.gamma))

                {

                   cmap_entries = make_gray_file_colormap(display);

                   data_encoding = P_FILE;

                }

                else

                   cmap_entries = make_gray_colormap(display);

                /* But if the input has alpha or transparency it must be removed

                 */

                if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||

                   png_ptr->num_trans > 0)

                {

                   png_color_16 c;

                   png_uint_32 gray = back_g;

                   /* We need to ensure that the application background exists in

                    * the colormap and that completely transparent pixels map to

                    * it.  Achieve this simply by ensuring that the entry

                    * selected for the background really is the background color.

                    */

                   if (data_encoding == P_FILE) /* from the fixup above */

                   {

                      /* The app supplied a gray which is in output_encoding, we

                       * need to convert it to a value of the input (P_FILE)

                       * encoding then set this palette entry to the required

                       * output encoding.

                       */

                      if (output_encoding == P_sRGB)

                         gray = png_sRGB_table[gray]; /* now P_LINEAR */

                      gray = PNG_DIV257(png_gamma_16bit_correct(gray,

                         png_ptr->colorspace.gamma)); /* now P_FILE */

                      /* And make sure the corresponding palette entry contains

                       * exactly the required sRGB value.

                       */

                      png_create_colormap_entry(display, gray, back_g, back_g,

                         back_g, 0/*unused*/, output_encoding);

                   }

                   else if (output_encoding == P_LINEAR)

                   {

                      gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                      /* And make sure the corresponding palette entry matches.

                       */

                      png_create_colormap_entry(display, gray, back_g, back_g,

                         back_g, 0/*unused*/, P_LINEAR);

                   }

                   /* The background passed to libpng, however, must be the

                    * output (normally sRGB) value.

                    */

                   c.index = 0; /*unused*/

                   c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                   /* NOTE: the following is apparently a bug in libpng. Without

                    * it the transparent color recognition in

                    * png_set_background_fixed seems to go wrong.

                    */

                   expand_tRNS = 1;

                   png_set_background_fixed(png_ptr, &c,

                      PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,