jquant1.cpp

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "mrpt_jpeglib.h"
#include <mrpt/utils/mrpt_macros.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;
        static const int RGB_order[3] = {RGB_GREEN, RGB_RED, RGB_BLUE};

        /* 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 */
{
        MRPT_UNUSED_PARAM(cinfo);
        MRPT_UNUSED_PARAM(ci);
        /* 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 */
{
        MRPT_UNUSED_PARAM(cinfo);
        MRPT_UNUSED_PARAM(ci);
        /* 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 = nullptr; /* search for matching prior component */
                for (j = 0; j < i; j++)
                {
                        if (nci == cquantize->Ncolors[j])
                        {
                                odither = cquantize->odither[j];
                                break;
                        }
                }
                if (odither == nullptr) /* 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;
        int pixcode, ci;
        JSAMPROW ptrin, ptrout;
        int row;
        JDIMENSION col;
        JDIMENSION width = cinfo->output_width;
        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;
        int pixcode;
        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;
        JSAMPROW input_ptr;
        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;
        int pixcode;
        JSAMPROW input_ptr;
        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;
        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;
        FSERRPTR errorptr; /* => fserrors[] at column before current */
        JSAMPROW input_ptr;
        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)
{
        MRPT_UNUSED_PARAM(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] == nullptr) 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] == nullptr) 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) { /* 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] = nullptr; /* Flag FS workspace not allocated */
        cquantize->odither[0] =
                nullptr; /* 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 */