/*

 * 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, 2015, D. R. Commander.

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

 * 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.

 */

#if BITS_IN_JSAMPLE == 8

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

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

#else

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

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

#endif

typedef FSERROR *FSERRPTR;  /* pointer to error array */

/* 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) (((JLONG) 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) (((JLONG) (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;

  JLONG 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 * ((JLONG) (ncolors - 1));

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

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

      num = ((JLONG) (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 *) 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 *) 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 *) 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 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 */