The Tor Browser / file revision

 /*

  * jquant1.c

  *

  * This file was part of the Independent JPEG Group's software:

  * Copyright (C) 1991-1996, Thomas G. Lane.

  * libjpeg-turbo Modifications:

  * Copyright (C) 2009, D. R. Commander

  * For conditions of distribution and use, see the accompanying README file.

  *

  * This file contains 1-pass color quantization (color mapping) routines.

  * These routines provide mapping to a fixed color map using equally spaced

  * color values.  Optional Floyd-Steinberg or ordered dithering is available.

  */

 #define JPEG_INTERNALS

 #include "jinclude.h"

 #include "jpeglib.h"

 #ifdef QUANT_1PASS_SUPPORTED

 /*

  * The main purpose of 1-pass quantization is to provide a fast, if not very

  * high quality, colormapped output capability.  A 2-pass quantizer usually

  * gives better visual quality; however, for quantized grayscale output this

  * quantizer is perfectly adequate.  Dithering is highly recommended with this

  * quantizer, though you can turn it off if you really want to.

  *

  * In 1-pass quantization the colormap must be chosen in advance of seeing the

  * image.  We use a map consisting of all combinations of Ncolors[i] color

  * values for the i'th component.  The Ncolors[] values are chosen so that

  * their product, the total number of colors, is no more than that requested.

  * (In most cases, the product will be somewhat less.)

  *

  * Since the colormap is orthogonal, the representative value for each color

  * component can be determined without considering the other components;

  * then these indexes can be combined into a colormap index by a standard

  * N-dimensional-array-subscript calculation.  Most of the arithmetic involved

  * can be precalculated and stored in the lookup table colorindex[].

  * colorindex[i][j] maps pixel value j in component i to the nearest

  * representative value (grid plane) for that component; this index is

  * multiplied by the array stride for component i, so that the

  * index of the colormap entry closest to a given pixel value is just

  *    sum( colorindex[component-number][pixel-component-value] )

  * Aside from being fast, this scheme allows for variable spacing between

  * representative values with no additional lookup cost.

  *

  * If gamma correction has been applied in color conversion, it might be wise

  * to adjust the color grid spacing so that the representative colors are

  * equidistant in linear space.  At this writing, gamma correction is not

  * implemented by jdcolor, so nothing is done here.

  */

 /* Declarations for ordered dithering.

  *

  * We use a standard 16x16 ordered dither array.  The basic concept of ordered

  * dithering is described in many references, for instance Dale Schumacher's

  * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).

  * In place of Schumacher's comparisons against a "threshold" value, we add a

  * "dither" value to the input pixel and then round the result to the nearest

  * output value.  The dither value is equivalent to (0.5 - threshold) times

  * the distance between output values.  For ordered dithering, we assume that

  * the output colors are equally spaced; if not, results will probably be

  * worse, since the dither may be too much or too little at a given point.

  *

  * The normal calculation would be to form pixel value + dither, range-limit

  * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.

  * We can skip the separate range-limiting step by extending the colorindex

  * table in both directions.

  */

 #define ODITHER_SIZE  16	/* dimension of dither matrix */

 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */

 #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE)	/* # cells in matrix */

 #define ODITHER_MASK  (ODITHER_SIZE-1) /* mask for wrapping around counters */

 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];

 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];

 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {

   /* Bayer's order-4 dither array.  Generated by the code given in

    * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.

    * The values in this array must range from 0 to ODITHER_CELLS-1.

    */

   {   0,192, 48,240, 12,204, 60,252,  3,195, 51,243, 15,207, 63,255 },

   { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },

   {  32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },

   { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },

   {   8,200, 56,248,  4,196, 52,244, 11,203, 59,251,  7,199, 55,247 },

   { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },

   {  40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },

   { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },

   {   2,194, 50,242, 14,206, 62,254,  1,193, 49,241, 13,205, 61,253 },

   { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },

   {  34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },

   { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },

   {  10,202, 58,250,  6,198, 54,246,  9,201, 57,249,  5,197, 53,245 },

   { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },

   {  42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },

   { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }

 };

 /* Declarations for Floyd-Steinberg dithering.

  *

  * Errors are accumulated into the array fserrors[], at a resolution of

  * 1/16th of a pixel count.  The error at a given pixel is propagated

  * to its not-yet-processed neighbors using the standard F-S fractions,

  *		...	(here)	7/16

  *		3/16	5/16	1/16

  * We work left-to-right on even rows, right-to-left on odd rows.

  *

  * We can get away with a single array (holding one row's worth of errors)

  * by using it to store the current row's errors at pixel columns not yet

  * processed, but the next row's errors at columns already processed.  We

  * need only a few extra variables to hold the errors immediately around the

  * current column.  (If we are lucky, those variables are in registers, but

  * even if not, they're probably cheaper to access than array elements are.)

  *

  * The fserrors[] array is indexed [component#][position].

  * We provide (#columns + 2) entries per component; the extra entry at each

  * end saves us from special-casing the first and last pixels.

  *

  * Note: on a wide image, we might not have enough room in a PC's near data

  * segment to hold the error array; so it is allocated with alloc_large.

  */

 #if BITS_IN_JSAMPLE == 8

 typedef INT16 FSERROR;		/* 16 bits should be enough */

 typedef int LOCFSERROR;		/* use 'int' for calculation temps */

 #else

 typedef INT32 FSERROR;		/* may need more than 16 bits */

 typedef INT32 LOCFSERROR;	/* be sure calculation temps are big enough */

 #endif

 typedef FSERROR FAR *FSERRPTR;	/* pointer to error array (in FAR storage!) */

 /* Private subobject */

 #define MAX_Q_COMPS 4		/* max components I can handle */

 typedef struct {

   struct jpeg_color_quantizer pub; /* public fields */

   /* Initially allocated colormap is saved here */

   JSAMPARRAY sv_colormap;	/* The color map as a 2-D pixel array */

   int sv_actual;		/* number of entries in use */

   JSAMPARRAY colorindex;	/* Precomputed mapping for speed */

   /* colorindex[i][j] = index of color closest to pixel value j in component i,

    * premultiplied as described above.  Since colormap indexes must fit into

    * JSAMPLEs, the entries of this array will too.

    */

   boolean is_padded;		/* is the colorindex padded for odither? */

   int Ncolors[MAX_Q_COMPS];	/* # of values alloced to each component */

   /* Variables for ordered dithering */

   int row_index;		/* cur row's vertical index in dither matrix */

   ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */

   /* Variables for Floyd-Steinberg dithering */

   FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */

   boolean on_odd_row;		/* flag to remember which row we are on */

 } my_cquantizer;

 typedef my_cquantizer * my_cquantize_ptr;

 /*

  * Policy-making subroutines for create_colormap and create_colorindex.

  * These routines determine the colormap to be used.  The rest of the module

  * only assumes that the colormap is orthogonal.

  *

  *  * select_ncolors decides how to divvy up the available colors

  *    among the components.

  *  * output_value defines the set of representative values for a component.

  *  * largest_input_value defines the mapping from input values to

  *    representative values for a component.

  * Note that the latter two routines may impose different policies for

  * different components, though this is not currently done.

  */

 LOCAL(int)

 select_ncolors (j_decompress_ptr cinfo, int Ncolors[])

 /* Determine allocation of desired colors to components, */

 /* and fill in Ncolors[] array to indicate choice. */

 /* Return value is total number of colors (product of Ncolors[] values). */

 {

   int nc = cinfo->out_color_components; /* number of color components */

   int max_colors = cinfo->desired_number_of_colors;

   int total_colors, iroot, i, j;

   boolean changed;

   long temp;

   int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };

   RGB_order[0] = rgb_green[cinfo->out_color_space];

   RGB_order[1] = rgb_red[cinfo->out_color_space];

   RGB_order[2] = rgb_blue[cinfo->out_color_space];

   /* We can allocate at least the nc'th root of max_colors per component. */

   /* Compute floor(nc'th root of max_colors). */

   iroot = 1;

   do {

     iroot++;

     temp = iroot;		/* set temp = iroot ** nc */

     for (i = 1; i < nc; i++)

       temp *= iroot;

   } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */

   iroot--;			/* now iroot = floor(root) */

   /* Must have at least 2 color values per component */

   if (iroot < 2)

     ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);

   /* Initialize to iroot color values for each component */

   total_colors = 1;

   for (i = 0; i < nc; i++) {

     Ncolors[i] = iroot;

     total_colors *= iroot;

   }

   /* We may be able to increment the count for one or more components without

    * exceeding max_colors, though we know not all can be incremented.

    * Sometimes, the first component can be incremented more than once!

    * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)

    * In RGB colorspace, try to increment G first, then R, then B.

    */

   do {

     changed = FALSE;

     for (i = 0; i < nc; i++) {

       j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);

       /* calculate new total_colors if Ncolors[j] is incremented */

       temp = total_colors / Ncolors[j];

       temp *= Ncolors[j]+1;	/* done in long arith to avoid oflo */

       if (temp > (long) max_colors)

 	break;			/* won't fit, done with this pass */

       Ncolors[j]++;		/* OK, apply the increment */

       total_colors = (int) temp;

       changed = TRUE;

     }

   } while (changed);

   return total_colors;

 }

 LOCAL(int)

 output_value (j_decompress_ptr cinfo, int ci, int j, int maxj)

 /* Return j'th output value, where j will range from 0 to maxj */

 /* The output values must fall in 0..MAXJSAMPLE in increasing order */

 {

   /* We always provide values 0 and MAXJSAMPLE for each component;

    * any additional values are equally spaced between these limits.

    * (Forcing the upper and lower values to the limits ensures that

    * dithering can't produce a color outside the selected gamut.)

    */

   return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);

 }

 LOCAL(int)

 largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)

 /* Return largest input value that should map to j'th output value */

 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */

 {

   /* Breakpoints are halfway between values returned by output_value */

   return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));

 }

 /*

  * Create the colormap.

  */

 LOCAL(void)

 create_colormap (j_decompress_ptr cinfo)

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   JSAMPARRAY colormap;		/* Created colormap */

   int total_colors;		/* Number of distinct output colors */

   int i,j,k, nci, blksize, blkdist, ptr, val;

   /* Select number of colors for each component */

   total_colors = select_ncolors(cinfo, cquantize->Ncolors);

   /* Report selected color counts */

   if (cinfo->out_color_components == 3)

     TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,

 	     total_colors, cquantize->Ncolors[0],

 	     cquantize->Ncolors[1], cquantize->Ncolors[2]);

   else

     TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);

   /* Allocate and fill in the colormap. */

   /* The colors are ordered in the map in standard row-major order, */

   /* i.e. rightmost (highest-indexed) color changes most rapidly. */

   colormap = (*cinfo->mem->alloc_sarray)

     ((j_common_ptr) cinfo, JPOOL_IMAGE,

      (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);

   /* blksize is number of adjacent repeated entries for a component */

   /* blkdist is distance between groups of identical entries for a component */

   blkdist = total_colors;

   for (i = 0; i < cinfo->out_color_components; i++) {

     /* fill in colormap entries for i'th color component */

     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */

     blksize = blkdist / nci;

     for (j = 0; j < nci; j++) {

       /* Compute j'th output value (out of nci) for component */

       val = output_value(cinfo, i, j, nci-1);

       /* Fill in all colormap entries that have this value of this component */

       for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {

 	/* fill in blksize entries beginning at ptr */

 	for (k = 0; k < blksize; k++)

 	  colormap[i][ptr+k] = (JSAMPLE) val;

       }

     }

     blkdist = blksize;		/* blksize of this color is blkdist of next */

   }

   /* Save the colormap in private storage,

    * where it will survive color quantization mode changes.

    */

   cquantize->sv_colormap = colormap;

   cquantize->sv_actual = total_colors;

 }

 /*

  * Create the color index table.

  */

 LOCAL(void)

 create_colorindex (j_decompress_ptr cinfo)

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   JSAMPROW indexptr;

   int i,j,k, nci, blksize, val, pad;

   /* For ordered dither, we pad the color index tables by MAXJSAMPLE in

    * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).

    * This is not necessary in the other dithering modes.  However, we

    * flag whether it was done in case user changes dithering mode.

    */

   if (cinfo->dither_mode == JDITHER_ORDERED) {

     pad = MAXJSAMPLE*2;

     cquantize->is_padded = TRUE;

   } else {

     pad = 0;

     cquantize->is_padded = FALSE;

   }

   cquantize->colorindex = (*cinfo->mem->alloc_sarray)

     ((j_common_ptr) cinfo, JPOOL_IMAGE,

      (JDIMENSION) (MAXJSAMPLE+1 + pad),

      (JDIMENSION) cinfo->out_color_components);

   /* blksize is number of adjacent repeated entries for a component */

   blksize = cquantize->sv_actual;

   for (i = 0; i < cinfo->out_color_components; i++) {

     /* fill in colorindex entries for i'th color component */

     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */

     blksize = blksize / nci;

     /* adjust colorindex pointers to provide padding at negative indexes. */

     if (pad)

       cquantize->colorindex[i] += MAXJSAMPLE;

     /* in loop, val = index of current output value, */

     /* and k = largest j that maps to current val */

     indexptr = cquantize->colorindex[i];

     val = 0;

     k = largest_input_value(cinfo, i, 0, nci-1);

     for (j = 0; j <= MAXJSAMPLE; j++) {

       while (j > k)		/* advance val if past boundary */

 	k = largest_input_value(cinfo, i, ++val, nci-1);

       /* premultiply so that no multiplication needed in main processing */

       indexptr[j] = (JSAMPLE) (val * blksize);

     }

     /* Pad at both ends if necessary */

     if (pad)

       for (j = 1; j <= MAXJSAMPLE; j++) {

 	indexptr[-j] = indexptr[0];

 	indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];

       }

   }

 }

 /*

  * Create an ordered-dither array for a component having ncolors

  * distinct output values.

  */

 LOCAL(ODITHER_MATRIX_PTR)

 make_odither_array (j_decompress_ptr cinfo, int ncolors)

 {

   ODITHER_MATRIX_PTR odither;

   int j,k;

   INT32 num,den;

   odither = (ODITHER_MATRIX_PTR)

     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				SIZEOF(ODITHER_MATRIX));

   /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).

    * Hence the dither value for the matrix cell with fill order f

    * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).

    * On 16-bit-int machine, be careful to avoid overflow.

    */

   den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1));

   for (j = 0; j < ODITHER_SIZE; j++) {

     for (k = 0; k < ODITHER_SIZE; k++) {

       num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))

 	    * MAXJSAMPLE;

       /* Ensure round towards zero despite C's lack of consistency

        * about rounding negative values in integer division...

        */

       odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);

     }

   }

   return odither;

 }

 /*

  * Create the ordered-dither tables.

  * Components having the same number of representative colors may 

  * share a dither table.

  */

 LOCAL(void)

 create_odither_tables (j_decompress_ptr cinfo)

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   ODITHER_MATRIX_PTR odither;

   int i, j, nci;

   for (i = 0; i < cinfo->out_color_components; i++) {

     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */

     odither = NULL;		/* search for matching prior component */

     for (j = 0; j < i; j++) {

       if (nci == cquantize->Ncolors[j]) {

 	odither = cquantize->odither[j];

 	break;

       }

     }

     if (odither == NULL)	/* need a new table? */

       odither = make_odither_array(cinfo, nci);

     cquantize->odither[i] = odither;

   }

 }

 /*

  * Map some rows of pixels to the output colormapped representation.

  */

 METHODDEF(void)

 color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,

 		JSAMPARRAY output_buf, int num_rows)

 /* General case, no dithering */

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   JSAMPARRAY colorindex = cquantize->colorindex;

   register int pixcode, ci;

   register JSAMPROW ptrin, ptrout;

   int row;

   JDIMENSION col;

   JDIMENSION width = cinfo->output_width;

   register int nc = cinfo->out_color_components;

   for (row = 0; row < num_rows; row++) {

     ptrin = input_buf[row];

     ptrout = output_buf[row];

     for (col = width; col > 0; col--) {

       pixcode = 0;

       for (ci = 0; ci < nc; ci++) {

 	pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);

       }

       *ptrout++ = (JSAMPLE) pixcode;

     }

   }

 }

 METHODDEF(void)

 color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,

 		 JSAMPARRAY output_buf, int num_rows)

 /* Fast path for out_color_components==3, no dithering */

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   register int pixcode;

   register JSAMPROW ptrin, ptrout;

   JSAMPROW colorindex0 = cquantize->colorindex[0];

   JSAMPROW colorindex1 = cquantize->colorindex[1];

   JSAMPROW colorindex2 = cquantize->colorindex[2];

   int row;

   JDIMENSION col;

   JDIMENSION width = cinfo->output_width;

   for (row = 0; row < num_rows; row++) {

     ptrin = input_buf[row];

     ptrout = output_buf[row];

     for (col = width; col > 0; col--) {

       pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);

       pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);

       pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);

       *ptrout++ = (JSAMPLE) pixcode;

     }

   }

 }

 METHODDEF(void)

 quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,

 		     JSAMPARRAY output_buf, int num_rows)

 /* General case, with ordered dithering */

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   register JSAMPROW input_ptr;

   register JSAMPROW output_ptr;

   JSAMPROW colorindex_ci;

   int * dither;			/* points to active row of dither matrix */

   int row_index, col_index;	/* current indexes into dither matrix */

   int nc = cinfo->out_color_components;

   int ci;

   int row;

   JDIMENSION col;

   JDIMENSION width = cinfo->output_width;

   for (row = 0; row < num_rows; row++) {

     /* Initialize output values to 0 so can process components separately */

     jzero_far((void FAR *) output_buf[row],

 	      (size_t) (width * SIZEOF(JSAMPLE)));

     row_index = cquantize->row_index;

     for (ci = 0; ci < nc; ci++) {

       input_ptr = input_buf[row] + ci;

       output_ptr = output_buf[row];

       colorindex_ci = cquantize->colorindex[ci];

       dither = cquantize->odither[ci][row_index];

       col_index = 0;

       for (col = width; col > 0; col--) {

 	/* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,

 	 * select output value, accumulate into output code for this pixel.

 	 * Range-limiting need not be done explicitly, as we have extended

 	 * the colorindex table to produce the right answers for out-of-range

 	 * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the

 	 * required amount of padding.

 	 */

 	*output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];

 	input_ptr += nc;

 	output_ptr++;

 	col_index = (col_index + 1) & ODITHER_MASK;

       }

     }

     /* Advance row index for next row */

     row_index = (row_index + 1) & ODITHER_MASK;

     cquantize->row_index = row_index;

   }

 }

 METHODDEF(void)

 quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,

 		      JSAMPARRAY output_buf, int num_rows)

 /* Fast path for out_color_components==3, with ordered dithering */

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   register int pixcode;

   register JSAMPROW input_ptr;

   register JSAMPROW output_ptr;

   JSAMPROW colorindex0 = cquantize->colorindex[0];

   JSAMPROW colorindex1 = cquantize->colorindex[1];

   JSAMPROW colorindex2 = cquantize->colorindex[2];

   int * dither0;		/* points to active row of dither matrix */

   int * dither1;

   int * dither2;

   int row_index, col_index;	/* current indexes into dither matrix */

   int row;

   JDIMENSION col;

   JDIMENSION width = cinfo->output_width;

   for (row = 0; row < num_rows; row++) {

     row_index = cquantize->row_index;

     input_ptr = input_buf[row];

     output_ptr = output_buf[row];

     dither0 = cquantize->odither[0][row_index];

     dither1 = cquantize->odither[1][row_index];

     dither2 = cquantize->odither[2][row_index];

     col_index = 0;

     for (col = width; col > 0; col--) {

       pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +

 					dither0[col_index]]);

       pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +

 					dither1[col_index]]);

       pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +

 					dither2[col_index]]);

       *output_ptr++ = (JSAMPLE) pixcode;

       col_index = (col_index + 1) & ODITHER_MASK;

     }

     row_index = (row_index + 1) & ODITHER_MASK;

     cquantize->row_index = row_index;

   }

 }

 METHODDEF(void)

 quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,

 		    JSAMPARRAY output_buf, int num_rows)

 /* General case, with Floyd-Steinberg dithering */

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   register LOCFSERROR cur;	/* current error or pixel value */

   LOCFSERROR belowerr;		/* error for pixel below cur */

   LOCFSERROR bpreverr;		/* error for below/prev col */

   LOCFSERROR bnexterr;		/* error for below/next col */

   LOCFSERROR delta;

   register FSERRPTR errorptr;	/* => fserrors[] at column before current */

   register JSAMPROW input_ptr;

   register JSAMPROW output_ptr;

   JSAMPROW colorindex_ci;

   JSAMPROW colormap_ci;

   int pixcode;

   int nc = cinfo->out_color_components;

   int dir;			/* 1 for left-to-right, -1 for right-to-left */

   int dirnc;			/* dir * nc */

   int ci;

   int row;

   JDIMENSION col;

   JDIMENSION width = cinfo->output_width;

   JSAMPLE *range_limit = cinfo->sample_range_limit;

   SHIFT_TEMPS

   for (row = 0; row < num_rows; row++) {

     /* Initialize output values to 0 so can process components separately */

     jzero_far((void FAR *) output_buf[row],

 	      (size_t) (width * SIZEOF(JSAMPLE)));

     for (ci = 0; ci < nc; ci++) {

       input_ptr = input_buf[row] + ci;

       output_ptr = output_buf[row];

       if (cquantize->on_odd_row) {

 	/* work right to left in this row */

 	input_ptr += (width-1) * nc; /* so point to rightmost pixel */

 	output_ptr += width-1;

 	dir = -1;

 	dirnc = -nc;

 	errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */

       } else {

 	/* work left to right in this row */

 	dir = 1;

 	dirnc = nc;

 	errorptr = cquantize->fserrors[ci]; /* => entry before first column */

       }

       colorindex_ci = cquantize->colorindex[ci];

       colormap_ci = cquantize->sv_colormap[ci];

       /* Preset error values: no error propagated to first pixel from left */

       cur = 0;

       /* and no error propagated to row below yet */

       belowerr = bpreverr = 0;

       for (col = width; col > 0; col--) {

 	/* cur holds the error propagated from the previous pixel on the

 	 * current line.  Add the error propagated from the previous line

 	 * to form the complete error correction term for this pixel, and

 	 * round the error term (which is expressed * 16) to an integer.

 	 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct

 	 * for either sign of the error value.

 	 * Note: errorptr points to *previous* column's array entry.

 	 */

 	cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);

 	/* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.

 	 * The maximum error is +- MAXJSAMPLE; this sets the required size

 	 * of the range_limit array.

 	 */

 	cur += GETJSAMPLE(*input_ptr);

 	cur = GETJSAMPLE(range_limit[cur]);

 	/* Select output value, accumulate into output code for this pixel */

 	pixcode = GETJSAMPLE(colorindex_ci[cur]);

 	*output_ptr += (JSAMPLE) pixcode;

 	/* Compute actual representation error at this pixel */

 	/* Note: we can do this even though we don't have the final */

 	/* pixel code, because the colormap is orthogonal. */

 	cur -= GETJSAMPLE(colormap_ci[pixcode]);

 	/* Compute error fractions to be propagated to adjacent pixels.

 	 * Add these into the running sums, and simultaneously shift the

 	 * next-line error sums left by 1 column.

 	 */

 	bnexterr = cur;

 	delta = cur * 2;

 	cur += delta;		/* form error * 3 */

 	errorptr[0] = (FSERROR) (bpreverr + cur);

 	cur += delta;		/* form error * 5 */

 	bpreverr = belowerr + cur;

 	belowerr = bnexterr;

 	cur += delta;		/* form error * 7 */

 	/* At this point cur contains the 7/16 error value to be propagated

 	 * to the next pixel on the current line, and all the errors for the

 	 * next line have been shifted over. We are therefore ready to move on.

 	 */

 	input_ptr += dirnc;	/* advance input ptr to next column */

 	output_ptr += dir;	/* advance output ptr to next column */

 	errorptr += dir;	/* advance errorptr to current column */

       }

       /* Post-loop cleanup: we must unload the final error value into the

        * final fserrors[] entry.  Note we need not unload belowerr because

        * it is for the dummy column before or after the actual array.

        */

       errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */

     }

     cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);

   }

 }

 /*

  * Allocate workspace for Floyd-Steinberg errors.

  */

 LOCAL(void)

 alloc_fs_workspace (j_decompress_ptr cinfo)

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   size_t arraysize;

   int i;

   arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));

   for (i = 0; i < cinfo->out_color_components; i++) {

     cquantize->fserrors[i] = (FSERRPTR)

       (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);

   }

 }

 /*

  * Initialize for one-pass color quantization.

  */

 METHODDEF(void)

 start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)

 {

   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;

   size_t arraysize;

   int i;

   /* Install my colormap. */

   cinfo->colormap = cquantize->sv_colormap;

   cinfo->actual_number_of_colors = cquantize->sv_actual;

   /* Initialize for desired dithering mode. */

   switch (cinfo->dither_mode) {

   case JDITHER_NONE:

     if (cinfo->out_color_components == 3)

       cquantize->pub.color_quantize = color_quantize3;

     else

       cquantize->pub.color_quantize = color_quantize;

     break;

   case JDITHER_ORDERED:

     if (cinfo->out_color_components == 3)

       cquantize->pub.color_quantize = quantize3_ord_dither;

     else

       cquantize->pub.color_quantize = quantize_ord_dither;

     cquantize->row_index = 0;	/* initialize state for ordered dither */

     /* If user changed to ordered dither from another mode,

      * we must recreate the color index table with padding.

      * This will cost extra space, but probably isn't very likely.

      */

     if (! cquantize->is_padded)

       create_colorindex(cinfo);

     /* Create ordered-dither tables if we didn't already. */

     if (cquantize->odither[0] == NULL)

       create_odither_tables(cinfo);

     break;

   case JDITHER_FS:

     cquantize->pub.color_quantize = quantize_fs_dither;

     cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */

     /* Allocate Floyd-Steinberg workspace if didn't already. */

     if (cquantize->fserrors[0] == NULL)

       alloc_fs_workspace(cinfo);

     /* Initialize the propagated errors to zero. */

     arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));

     for (i = 0; i < cinfo->out_color_components; i++)

       jzero_far((void FAR *) cquantize->fserrors[i], arraysize);

     break;

   default:

     ERREXIT(cinfo, JERR_NOT_COMPILED);

     break;

   }

 }

 /*

  * Finish up at the end of the pass.

  */

 METHODDEF(void)

 finish_pass_1_quant (j_decompress_ptr cinfo)

 {

   /* no work in 1-pass case */

 }

 /*

  * Switch to a new external colormap between output passes.

  * Shouldn't get to this module!

  */

 METHODDEF(void)

 new_color_map_1_quant (j_decompress_ptr cinfo)

 {

   ERREXIT(cinfo, JERR_MODE_CHANGE);

 }

 /*

  * Module initialization routine for 1-pass color quantization.

  */

 GLOBAL(void)

 jinit_1pass_quantizer (j_decompress_ptr cinfo)

 {

   my_cquantize_ptr cquantize;

   cquantize = (my_cquantize_ptr)

     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				SIZEOF(my_cquantizer));

   cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;

   cquantize->pub.start_pass = start_pass_1_quant;

   cquantize->pub.finish_pass = finish_pass_1_quant;

   cquantize->pub.new_color_map = new_color_map_1_quant;

   cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */

   cquantize->odither[0] = NULL;	/* Also flag odither arrays not allocated */

   /* Make sure my internal arrays won't overflow */

   if (cinfo->out_color_components > MAX_Q_COMPS)

     ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);

   /* Make sure colormap indexes can be represented by JSAMPLEs */

   if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))

     ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);

   /* Create the colormap and color index table. */

   create_colormap(cinfo);

   create_colorindex(cinfo);

   /* Allocate Floyd-Steinberg workspace now if requested.

    * We do this now since it is FAR storage and may affect the memory

    * manager's space calculations.  If the user changes to FS dither

    * mode in a later pass, we will allocate the space then, and will

    * possibly overrun the max_memory_to_use setting.

    */

   if (cinfo->dither_mode == JDITHER_FS)

     alloc_fs_workspace(cinfo);

 }

 #endif /* QUANT_1PASS_SUPPORTED */