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/*
* 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, 2022-2023, 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"
#include "jsamplecomp.h"
#if defined(QUANT_1PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16
/*
* 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 allocated 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 = (_JSAMPARRAY)(*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 = (_JSAMPARRAY)(*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 += colorindex[ci][*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 = colorindex0[*ptrin++];
pixcode += colorindex1[*ptrin++];
pixcode += colorindex2[*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[*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 = colorindex0[(*input_ptr++) + dither0[col_index]];
pixcode += colorindex1[(*input_ptr++) + dither1[col_index]];
pixcode += colorindex2[(*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 = (_JSAMPLE *)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 += *input_ptr;
cur = range_limit[cur];
/* Select output value, accumulate into output code for this pixel */
pixcode = 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 -= 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 = (JSAMPARRAY)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;
if (cinfo->data_precision != BITS_IN_JSAMPLE)
ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
/* Color quantization is not supported with lossless JPEG images */
if (cinfo->master->lossless)
ERREXIT(cinfo, JERR_NOTIMPL);
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 /* defined(QUANT_1PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16 */
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