ref: 290c921d1d01119b7d4550770da06c491508508f
dir: /sys/src/cmd/gs/jpeg/jquant1.c/
/*
* jquant1.c
*
* Copyright (C) 1991-1996, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains 1-pass color quantization (color mapping) routines.
* These routines provide mapping to a fixed color map using equally spaced
* color values. Optional Floyd-Steinberg or ordered dithering is available.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#ifdef QUANT_1PASS_SUPPORTED
/*
* The main purpose of 1-pass quantization is to provide a fast, if not very
* high quality, colormapped output capability. A 2-pass quantizer usually
* gives better visual quality; however, for quantized grayscale output this
* quantizer is perfectly adequate. Dithering is highly recommended with this
* quantizer, though you can turn it off if you really want to.
*
* In 1-pass quantization the colormap must be chosen in advance of seeing the
* image. We use a map consisting of all combinations of Ncolors[i] color
* values for the i'th component. The Ncolors[] values are chosen so that
* their product, the total number of colors, is no more than that requested.
* (In most cases, the product will be somewhat less.)
*
* Since the colormap is orthogonal, the representative value for each color
* component can be determined without considering the other components;
* then these indexes can be combined into a colormap index by a standard
* N-dimensional-array-subscript calculation. Most of the arithmetic involved
* can be precalculated and stored in the lookup table colorindex[].
* colorindex[i][j] maps pixel value j in component i to the nearest
* representative value (grid plane) for that component; this index is
* multiplied by the array stride for component i, so that the
* index of the colormap entry closest to a given pixel value is just
* sum( colorindex[component-number][pixel-component-value] )
* Aside from being fast, this scheme allows for variable spacing between
* representative values with no additional lookup cost.
*
* If gamma correction has been applied in color conversion, it might be wise
* to adjust the color grid spacing so that the representative colors are
* equidistant in linear space. At this writing, gamma correction is not
* implemented by jdcolor, so nothing is done here.
*/
/* Declarations for ordered dithering.
*
* We use a standard 16x16 ordered dither array. The basic concept of ordered
* dithering is described in many references, for instance Dale Schumacher's
* chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
* In place of Schumacher's comparisons against a "threshold" value, we add a
* "dither" value to the input pixel and then round the result to the nearest
* output value. The dither value is equivalent to (0.5 - threshold) times
* the distance between output values. For ordered dithering, we assume that
* the output colors are equally spaced; if not, results will probably be
* worse, since the dither may be too much or too little at a given point.
*
* The normal calculation would be to form pixel value + dither, range-limit
* this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
* We can skip the separate range-limiting step by extending the colorindex
* table in both directions.
*/
#define ODITHER_SIZE 16 /* dimension of dither matrix */
/* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
#define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE) /* # cells in matrix */
#define ODITHER_MASK (ODITHER_SIZE-1) /* mask for wrapping around counters */
typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
/* Bayer's order-4 dither array. Generated by the code given in
* Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
* The values in this array must range from 0 to ODITHER_CELLS-1.
*/
{ 0,192, 48,240, 12,204, 60,252, 3,195, 51,243, 15,207, 63,255 },
{ 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
{ 32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
{ 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
{ 8,200, 56,248, 4,196, 52,244, 11,203, 59,251, 7,199, 55,247 },
{ 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
{ 40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
{ 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
{ 2,194, 50,242, 14,206, 62,254, 1,193, 49,241, 13,205, 61,253 },
{ 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
{ 34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
{ 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
{ 10,202, 58,250, 6,198, 54,246, 9,201, 57,249, 5,197, 53,245 },
{ 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
{ 42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
{ 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
};
/* Declarations for Floyd-Steinberg dithering.
*
* Errors are accumulated into the array fserrors[], at a resolution of
* 1/16th of a pixel count. The error at a given pixel is propagated
* to its not-yet-processed neighbors using the standard F-S fractions,
* ... (here) 7/16
* 3/16 5/16 1/16
* We work left-to-right on even rows, right-to-left on odd rows.
*
* We can get away with a single array (holding one row's worth of errors)
* by using it to store the current row's errors at pixel columns not yet
* processed, but the next row's errors at columns already processed. We
* need only a few extra variables to hold the errors immediately around the
* current column. (If we are lucky, those variables are in registers, but
* even if not, they're probably cheaper to access than array elements are.)
*
* The fserrors[] array is indexed [component#][position].
* We provide (#columns + 2) entries per component; the extra entry at each
* end saves us from special-casing the first and last pixels.
*
* Note: on a wide image, we might not have enough room in a PC's near data
* segment to hold the error array; so it is allocated with alloc_large.
*/
#if BITS_IN_JSAMPLE == 8
typedef INT16 FSERROR; /* 16 bits should be enough */
typedef int LOCFSERROR; /* use 'int' for calculation temps */
#else
typedef INT32 FSERROR; /* may need more than 16 bits */
typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */
#endif
typedef FSERROR FAR *FSERRPTR; /* pointer to error array (in FAR storage!) */
/* Private subobject */
#define MAX_Q_COMPS 4 /* max components I can handle */
typedef struct {
struct jpeg_color_quantizer pub; /* public fields */
/* Initially allocated colormap is saved here */
JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */
int sv_actual; /* number of entries in use */
JSAMPARRAY colorindex; /* Precomputed mapping for speed */
/* colorindex[i][j] = index of color closest to pixel value j in component i,
* premultiplied as described above. Since colormap indexes must fit into
* JSAMPLEs, the entries of this array will too.
*/
boolean is_padded; /* is the colorindex padded for odither? */
int Ncolors[MAX_Q_COMPS]; /* # of values alloced to each component */
/* Variables for ordered dithering */
int row_index; /* cur row's vertical index in dither matrix */
ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */
/* Variables for Floyd-Steinberg dithering */
FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */
boolean on_odd_row; /* flag to remember which row we are on */
} my_cquantizer;
typedef my_cquantizer * my_cquantize_ptr;
/*
* Policy-making subroutines for create_colormap and create_colorindex.
* These routines determine the colormap to be used. The rest of the module
* only assumes that the colormap is orthogonal.
*
* * select_ncolors decides how to divvy up the available colors
* among the components.
* * output_value defines the set of representative values for a component.
* * largest_input_value defines the mapping from input values to
* representative values for a component.
* Note that the latter two routines may impose different policies for
* different components, though this is not currently done.
*/
LOCAL(int)
select_ncolors (j_decompress_ptr cinfo, int Ncolors[])
/* Determine allocation of desired colors to components, */
/* and fill in Ncolors[] array to indicate choice. */
/* Return value is total number of colors (product of Ncolors[] values). */
{
int nc = cinfo->out_color_components; /* number of color components */
int max_colors = cinfo->desired_number_of_colors;
int total_colors, iroot, i, j;
boolean changed;
long temp;
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 */
{
/* We always provide values 0 and MAXJSAMPLE for each component;
* any additional values are equally spaced between these limits.
* (Forcing the upper and lower values to the limits ensures that
* dithering can't produce a color outside the selected gamut.)
*/
return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);
}
LOCAL(int)
largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
/* Return largest input value that should map to j'th output value */
/* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
{
/* Breakpoints are halfway between values returned by output_value */
return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
}
/*
* Create the colormap.
*/
LOCAL(void)
create_colormap (j_decompress_ptr cinfo)
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
JSAMPARRAY colormap; /* Created colormap */
int total_colors; /* Number of distinct output colors */
int i,j,k, nci, blksize, blkdist, ptr, val;
/* Select number of colors for each component */
total_colors = select_ncolors(cinfo, cquantize->Ncolors);
/* Report selected color counts */
if (cinfo->out_color_components == 3)
TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,
total_colors, cquantize->Ncolors[0],
cquantize->Ncolors[1], cquantize->Ncolors[2]);
else
TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);
/* Allocate and fill in the colormap. */
/* The colors are ordered in the map in standard row-major order, */
/* i.e. rightmost (highest-indexed) color changes most rapidly. */
colormap = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE,
(JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);
/* blksize is number of adjacent repeated entries for a component */
/* blkdist is distance between groups of identical entries for a component */
blkdist = total_colors;
for (i = 0; i < cinfo->out_color_components; i++) {
/* fill in colormap entries for i'th color component */
nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
blksize = blkdist / nci;
for (j = 0; j < nci; j++) {
/* Compute j'th output value (out of nci) for component */
val = output_value(cinfo, i, j, nci-1);
/* Fill in all colormap entries that have this value of this component */
for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {
/* fill in blksize entries beginning at ptr */
for (k = 0; k < blksize; k++)
colormap[i][ptr+k] = (JSAMPLE) val;
}
}
blkdist = blksize; /* blksize of this color is blkdist of next */
}
/* Save the colormap in private storage,
* where it will survive color quantization mode changes.
*/
cquantize->sv_colormap = colormap;
cquantize->sv_actual = total_colors;
}
/*
* Create the color index table.
*/
LOCAL(void)
create_colorindex (j_decompress_ptr cinfo)
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
JSAMPROW indexptr;
int i,j,k, nci, blksize, val, pad;
/* For ordered dither, we pad the color index tables by MAXJSAMPLE in
* each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
* This is not necessary in the other dithering modes. However, we
* flag whether it was done in case user changes dithering mode.
*/
if (cinfo->dither_mode == JDITHER_ORDERED) {
pad = MAXJSAMPLE*2;
cquantize->is_padded = TRUE;
} else {
pad = 0;
cquantize->is_padded = FALSE;
}
cquantize->colorindex = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE,
(JDIMENSION) (MAXJSAMPLE+1 + pad),
(JDIMENSION) cinfo->out_color_components);
/* blksize is number of adjacent repeated entries for a component */
blksize = cquantize->sv_actual;
for (i = 0; i < cinfo->out_color_components; i++) {
/* fill in colorindex entries for i'th color component */
nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
blksize = blksize / nci;
/* adjust colorindex pointers to provide padding at negative indexes. */
if (pad)
cquantize->colorindex[i] += MAXJSAMPLE;
/* in loop, val = index of current output value, */
/* and k = largest j that maps to current val */
indexptr = cquantize->colorindex[i];
val = 0;
k = largest_input_value(cinfo, i, 0, nci-1);
for (j = 0; j <= MAXJSAMPLE; j++) {
while (j > k) /* advance val if past boundary */
k = largest_input_value(cinfo, i, ++val, nci-1);
/* premultiply so that no multiplication needed in main processing */
indexptr[j] = (JSAMPLE) (val * blksize);
}
/* Pad at both ends if necessary */
if (pad)
for (j = 1; j <= MAXJSAMPLE; j++) {
indexptr[-j] = indexptr[0];
indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
}
}
}
/*
* Create an ordered-dither array for a component having ncolors
* distinct output values.
*/
LOCAL(ODITHER_MATRIX_PTR)
make_odither_array (j_decompress_ptr cinfo, int ncolors)
{
ODITHER_MATRIX_PTR odither;
int j,k;
INT32 num,den;
odither = (ODITHER_MATRIX_PTR)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(ODITHER_MATRIX));
/* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
* Hence the dither value for the matrix cell with fill order f
* (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
* On 16-bit-int machine, be careful to avoid overflow.
*/
den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1));
for (j = 0; j < ODITHER_SIZE; j++) {
for (k = 0; k < ODITHER_SIZE; k++) {
num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))
* MAXJSAMPLE;
/* Ensure round towards zero despite C's lack of consistency
* about rounding negative values in integer division...
*/
odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
}
}
return odither;
}
/*
* Create the ordered-dither tables.
* Components having the same number of representative colors may
* share a dither table.
*/
LOCAL(void)
create_odither_tables (j_decompress_ptr cinfo)
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
ODITHER_MATRIX_PTR odither;
int i, j, nci;
for (i = 0; i < cinfo->out_color_components; i++) {
nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
odither = NULL; /* search for matching prior component */
for (j = 0; j < i; j++) {
if (nci == cquantize->Ncolors[j]) {
odither = cquantize->odither[j];
break;
}
}
if (odither == NULL) /* need a new table? */
odither = make_odither_array(cinfo, nci);
cquantize->odither[i] = odither;
}
}
/*
* Map some rows of pixels to the output colormapped representation.
*/
METHODDEF(void)
color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
JSAMPARRAY output_buf, int num_rows)
/* General case, no dithering */
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
JSAMPARRAY colorindex = cquantize->colorindex;
register int pixcode, ci;
register JSAMPROW ptrin, ptrout;
int row;
JDIMENSION col;
JDIMENSION width = cinfo->output_width;
register int nc = cinfo->out_color_components;
for (row = 0; row < num_rows; row++) {
ptrin = input_buf[row];
ptrout = output_buf[row];
for (col = width; col > 0; col--) {
pixcode = 0;
for (ci = 0; ci < nc; ci++) {
pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
}
*ptrout++ = (JSAMPLE) pixcode;
}
}
}
METHODDEF(void)
color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
JSAMPARRAY output_buf, int num_rows)
/* Fast path for out_color_components==3, no dithering */
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
register int pixcode;
register JSAMPROW ptrin, ptrout;
JSAMPROW colorindex0 = cquantize->colorindex[0];
JSAMPROW colorindex1 = cquantize->colorindex[1];
JSAMPROW colorindex2 = cquantize->colorindex[2];
int row;
JDIMENSION col;
JDIMENSION width = cinfo->output_width;
for (row = 0; row < num_rows; row++) {
ptrin = input_buf[row];
ptrout = output_buf[row];
for (col = width; col > 0; col--) {
pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);
pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);
pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);
*ptrout++ = (JSAMPLE) pixcode;
}
}
}
METHODDEF(void)
quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
JSAMPARRAY output_buf, int num_rows)
/* General case, with ordered dithering */
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
register JSAMPROW input_ptr;
register JSAMPROW output_ptr;
JSAMPROW colorindex_ci;
int * dither; /* points to active row of dither matrix */
int row_index, col_index; /* current indexes into dither matrix */
int nc = cinfo->out_color_components;
int ci;
int row;
JDIMENSION col;
JDIMENSION width = cinfo->output_width;
for (row = 0; row < num_rows; row++) {
/* Initialize output values to 0 so can process components separately */
jzero_far((void FAR *) output_buf[row],
(size_t) (width * SIZEOF(JSAMPLE)));
row_index = cquantize->row_index;
for (ci = 0; ci < nc; ci++) {
input_ptr = input_buf[row] + ci;
output_ptr = output_buf[row];
colorindex_ci = cquantize->colorindex[ci];
dither = cquantize->odither[ci][row_index];
col_index = 0;
for (col = width; col > 0; col--) {
/* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
* select output value, accumulate into output code for this pixel.
* Range-limiting need not be done explicitly, as we have extended
* the colorindex table to produce the right answers for out-of-range
* inputs. The maximum dither is +- MAXJSAMPLE; this sets the
* required amount of padding.
*/
*output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
input_ptr += nc;
output_ptr++;
col_index = (col_index + 1) & ODITHER_MASK;
}
}
/* Advance row index for next row */
row_index = (row_index + 1) & ODITHER_MASK;
cquantize->row_index = row_index;
}
}
METHODDEF(void)
quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
JSAMPARRAY output_buf, int num_rows)
/* Fast path for out_color_components==3, with ordered dithering */
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
register int pixcode;
register JSAMPROW input_ptr;
register JSAMPROW output_ptr;
JSAMPROW colorindex0 = cquantize->colorindex[0];
JSAMPROW colorindex1 = cquantize->colorindex[1];
JSAMPROW colorindex2 = cquantize->colorindex[2];
int * dither0; /* points to active row of dither matrix */
int * dither1;
int * dither2;
int row_index, col_index; /* current indexes into dither matrix */
int row;
JDIMENSION col;
JDIMENSION width = cinfo->output_width;
for (row = 0; row < num_rows; row++) {
row_index = cquantize->row_index;
input_ptr = input_buf[row];
output_ptr = output_buf[row];
dither0 = cquantize->odither[0][row_index];
dither1 = cquantize->odither[1][row_index];
dither2 = cquantize->odither[2][row_index];
col_index = 0;
for (col = width; col > 0; col--) {
pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +
dither0[col_index]]);
pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +
dither1[col_index]]);
pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +
dither2[col_index]]);
*output_ptr++ = (JSAMPLE) pixcode;
col_index = (col_index + 1) & ODITHER_MASK;
}
row_index = (row_index + 1) & ODITHER_MASK;
cquantize->row_index = row_index;
}
}
METHODDEF(void)
quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
JSAMPARRAY output_buf, int num_rows)
/* General case, with Floyd-Steinberg dithering */
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
register LOCFSERROR cur; /* current error or pixel value */
LOCFSERROR belowerr; /* error for pixel below cur */
LOCFSERROR bpreverr; /* error for below/prev col */
LOCFSERROR bnexterr; /* error for below/next col */
LOCFSERROR delta;
register FSERRPTR errorptr; /* => fserrors[] at column before current */
register JSAMPROW input_ptr;
register JSAMPROW output_ptr;
JSAMPROW colorindex_ci;
JSAMPROW colormap_ci;
int pixcode;
int nc = cinfo->out_color_components;
int dir; /* 1 for left-to-right, -1 for right-to-left */
int dirnc; /* dir * nc */
int ci;
int row;
JDIMENSION col;
JDIMENSION width = cinfo->output_width;
JSAMPLE *range_limit = cinfo->sample_range_limit;
SHIFT_TEMPS
for (row = 0; row < num_rows; row++) {
/* Initialize output values to 0 so can process components separately */
jzero_far((void FAR *) output_buf[row],
(size_t) (width * SIZEOF(JSAMPLE)));
for (ci = 0; ci < nc; ci++) {
input_ptr = input_buf[row] + ci;
output_ptr = output_buf[row];
if (cquantize->on_odd_row) {
/* work right to left in this row */
input_ptr += (width-1) * nc; /* so point to rightmost pixel */
output_ptr += width-1;
dir = -1;
dirnc = -nc;
errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
} else {
/* work left to right in this row */
dir = 1;
dirnc = nc;
errorptr = cquantize->fserrors[ci]; /* => entry before first column */
}
colorindex_ci = cquantize->colorindex[ci];
colormap_ci = cquantize->sv_colormap[ci];
/* Preset error values: no error propagated to first pixel from left */
cur = 0;
/* and no error propagated to row below yet */
belowerr = bpreverr = 0;
for (col = width; col > 0; col--) {
/* cur holds the error propagated from the previous pixel on the
* current line. Add the error propagated from the previous line
* to form the complete error correction term for this pixel, and
* round the error term (which is expressed * 16) to an integer.
* RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
* for either sign of the error value.
* Note: errorptr points to *previous* column's array entry.
*/
cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
/* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
* The maximum error is +- MAXJSAMPLE; this sets the required size
* of the range_limit array.
*/
cur += GETJSAMPLE(*input_ptr);
cur = GETJSAMPLE(range_limit[cur]);
/* Select output value, accumulate into output code for this pixel */
pixcode = GETJSAMPLE(colorindex_ci[cur]);
*output_ptr += (JSAMPLE) pixcode;
/* Compute actual representation error at this pixel */
/* Note: we can do this even though we don't have the final */
/* pixel code, because the colormap is orthogonal. */
cur -= GETJSAMPLE(colormap_ci[pixcode]);
/* Compute error fractions to be propagated to adjacent pixels.
* Add these into the running sums, and simultaneously shift the
* next-line error sums left by 1 column.
*/
bnexterr = cur;
delta = cur * 2;
cur += delta; /* form error * 3 */
errorptr[0] = (FSERROR) (bpreverr + cur);
cur += delta; /* form error * 5 */
bpreverr = belowerr + cur;
belowerr = bnexterr;
cur += delta; /* form error * 7 */
/* At this point cur contains the 7/16 error value to be propagated
* to the next pixel on the current line, and all the errors for the
* next line have been shifted over. We are therefore ready to move on.
*/
input_ptr += dirnc; /* advance input ptr to next column */
output_ptr += dir; /* advance output ptr to next column */
errorptr += dir; /* advance errorptr to current column */
}
/* Post-loop cleanup: we must unload the final error value into the
* final fserrors[] entry. Note we need not unload belowerr because
* it is for the dummy column before or after the actual array.
*/
errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
}
cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
}
}
/*
* Allocate workspace for Floyd-Steinberg errors.
*/
LOCAL(void)
alloc_fs_workspace (j_decompress_ptr cinfo)
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
size_t arraysize;
int i;
arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
for (i = 0; i < cinfo->out_color_components; i++) {
cquantize->fserrors[i] = (FSERRPTR)
(*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
}
}
/*
* Initialize for one-pass color quantization.
*/
METHODDEF(void)
start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
{
my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
size_t arraysize;
int i;
/* Install my colormap. */
cinfo->colormap = cquantize->sv_colormap;
cinfo->actual_number_of_colors = cquantize->sv_actual;
/* Initialize for desired dithering mode. */
switch (cinfo->dither_mode) {
case JDITHER_NONE:
if (cinfo->out_color_components == 3)
cquantize->pub.color_quantize = color_quantize3;
else
cquantize->pub.color_quantize = color_quantize;
break;
case JDITHER_ORDERED:
if (cinfo->out_color_components == 3)
cquantize->pub.color_quantize = quantize3_ord_dither;
else
cquantize->pub.color_quantize = quantize_ord_dither;
cquantize->row_index = 0; /* initialize state for ordered dither */
/* If user changed to ordered dither from another mode,
* we must recreate the color index table with padding.
* This will cost extra space, but probably isn't very likely.
*/
if (! cquantize->is_padded)
create_colorindex(cinfo);
/* Create ordered-dither tables if we didn't already. */
if (cquantize->odither[0] == NULL)
create_odither_tables(cinfo);
break;
case JDITHER_FS:
cquantize->pub.color_quantize = quantize_fs_dither;
cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
/* Allocate Floyd-Steinberg workspace if didn't already. */
if (cquantize->fserrors[0] == NULL)
alloc_fs_workspace(cinfo);
/* Initialize the propagated errors to zero. */
arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
for (i = 0; i < cinfo->out_color_components; i++)
jzero_far((void FAR *) cquantize->fserrors[i], arraysize);
break;
default:
ERREXIT(cinfo, JERR_NOT_COMPILED);
break;
}
}
/*
* Finish up at the end of the pass.
*/
METHODDEF(void)
finish_pass_1_quant (j_decompress_ptr cinfo)
{
/* no work in 1-pass case */
}
/*
* Switch to a new external colormap between output passes.
* Shouldn't get to this module!
*/
METHODDEF(void)
new_color_map_1_quant (j_decompress_ptr cinfo)
{
ERREXIT(cinfo, JERR_MODE_CHANGE);
}
/*
* Module initialization routine for 1-pass color quantization.
*/
GLOBAL(void)
jinit_1pass_quantizer (j_decompress_ptr cinfo)
{
my_cquantize_ptr cquantize;
cquantize = (my_cquantize_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(my_cquantizer));
cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
cquantize->pub.start_pass = start_pass_1_quant;
cquantize->pub.finish_pass = finish_pass_1_quant;
cquantize->pub.new_color_map = new_color_map_1_quant;
cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
/* Make sure my internal arrays won't overflow */
if (cinfo->out_color_components > MAX_Q_COMPS)
ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
/* Make sure colormap indexes can be represented by JSAMPLEs */
if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);
/* Create the colormap and color index table. */
create_colormap(cinfo);
create_colorindex(cinfo);
/* Allocate Floyd-Steinberg workspace now if requested.
* We do this now since it is FAR storage and may affect the memory
* manager's space calculations. If the user changes to FS dither
* mode in a later pass, we will allocate the space then, and will
* possibly overrun the max_memory_to_use setting.
*/
if (cinfo->dither_mode == JDITHER_FS)
alloc_fs_workspace(cinfo);
}
#endif /* QUANT_1PASS_SUPPORTED */