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/*
* jquant1.c
*
* Copyright (C) 1991, 1992, 1993, 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 are invoked via the methods color_quantize
* and color_quant_init/term.
*/
#include "jinclude.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.
*
* This implementation quantizes in the output colorspace. This has a couple
* of disadvantages: each pixel must be individually color-converted, and if
* the color conversion includes gamma correction then quantization is done in
* a nonlinear space, which is less desirable. The major advantage is that
* with the usual output color spaces (RGB, grayscale) an orthogonal grid of
* representative colors can be used, thus permitting the very simple and fast
* color lookup scheme used here. The standard JPEG colorspace (YCbCr) cannot
* be effectively handled this way, because only about a quarter of an
* orthogonal grid would fall within the gamut of realizable colors. Another
* advantage is that when the user wants quantized grayscale output from a
* color JPEG file, this quantizer can provide a high-quality result with no
* special hacking.
*
* The gamma-correction problem could be eliminated by adjusting the grid
* spacing to counteract the gamma correction applied by color_convert.
* At this writing, gamma correction is not implemented by jdcolor, so
* nothing is done here.
*
* 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.
*/
#define MAX_COMPONENTS 4 /* max components I can handle */
static JSAMPARRAY colormap; /* The actual color map */
/* colormap[i][j] = value of i'th color component for output pixel value j */
static 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.
*/
static JSAMPARRAY input_buffer; /* color conversion workspace */
/* Since our input data is presented in the JPEG colorspace, we have to call
* color_convert to get it into the output colorspace. input_buffer is a
* one-row-high workspace for the result of color_convert.
*/
/* 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_medium.
*/
#ifdef EIGHT_BIT_SAMPLES
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!) */
static FSERRPTR fserrors[MAX_COMPONENTS]; /* accumulated errors */
static boolean on_odd_row; /* flag to remember which row we are on */
/*
* Policy-making subroutines for color_quant_init: 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 (decompress_info_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->color_out_comps; /* number of color components */
int max_colors = cinfo->desired_number_of_colors;
int total_colors, iroot, i;
long temp;
boolean changed;
/* 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->emethods, "Cannot quantize to fewer than %d colors",
(int) temp);
if (cinfo->out_color_space == CS_RGB && nc == 3) {
/* We provide a special policy for quantizing in RGB space.
* If 256 colors are requested, we allocate 8 red, 8 green, 4 blue levels;
* this corresponds to the common 3/3/2-bit scheme. For other totals,
* the counts are set so that the number of colors allocated to each
* component are roughly in the proportion R 3, G 4, B 2.
* For low color counts, it's easier to hardwire the optimal choices
* than try to tweak the algorithm to generate them.
*/
if (max_colors == 256) {
Ncolors[0] = 8; Ncolors[1] = 8; Ncolors[2] = 4;
return 256;
}
if (max_colors < 12) {
/* Fixed mapping for 8 colors */
Ncolors[0] = Ncolors[1] = Ncolors[2] = 2;
} else if (max_colors < 18) {
/* Fixed mapping for 12 colors */
Ncolors[0] = 2; Ncolors[1] = 3; Ncolors[2] = 2;
} else if (max_colors < 24) {
/* Fixed mapping for 18 colors */
Ncolors[0] = 3; Ncolors[1] = 3; Ncolors[2] = 2;
} else if (max_colors < 27) {
/* Fixed mapping for 24 colors */
Ncolors[0] = 3; Ncolors[1] = 4; Ncolors[2] = 2;
} else if (max_colors < 36) {
/* Fixed mapping for 27 colors */
Ncolors[0] = 3; Ncolors[1] = 3; Ncolors[2] = 3;
} else {
/* these weights are readily derived with a little algebra */
Ncolors[0] = (iroot * 266) >> 8; /* R weight is 1.0400 */
Ncolors[1] = (iroot * 355) >> 8; /* G weight is 1.3867 */
Ncolors[2] = (iroot * 177) >> 8; /* B weight is 0.6934 */
}
total_colors = Ncolors[0] * Ncolors[1] * Ncolors[2];
/* The above computation produces "floor" values, so we may be able to
* increment the count for one or more components without exceeding
* max_colors. We try in the order B, G, R.
*/
do {
changed = FALSE;
for (i = 2; i >= 0; i--) {
/* calculate new total_colors if Ncolors[i] is incremented */
temp = total_colors / Ncolors[i];
temp *= Ncolors[i]+1; /* done in long arith to avoid oflo */
if (temp <= (long) max_colors) {
Ncolors[i]++; /* OK, apply the increment */
total_colors = (int) temp;
changed = TRUE;
}
}
} while (changed); /* loop until no increment is possible */
} else {
/* For any colorspace besides RGB, treat all the components equally. */
/* 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.
*/
for (i = 0; i < nc; i++) {
/* calculate new total_colors if Ncolors[i] is incremented */
temp = total_colors / Ncolors[i];
temp *= Ncolors[i]+1; /* done in long arith to avoid oflo */
if (temp > (long) max_colors)
break; /* won't fit, done */
Ncolors[i]++; /* OK, apply the increment */
total_colors = (int) temp;
}
}
return total_colors;
}
LOCAL int
output_value (decompress_info_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 (decompress_info_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));
}
/*
* Initialize for one-pass color quantization.
*/
METHODDEF void
color_quant_init (decompress_info_ptr cinfo)
{
int total_colors; /* Number of distinct output colors */
int Ncolors[MAX_COMPONENTS]; /* # of values alloced to each component */
int i,j,k, nci, blksize, blkdist, ptr, val;
/* Make sure my internal arrays won't overflow */
if (cinfo->num_components > MAX_COMPONENTS ||
cinfo->color_out_comps > MAX_COMPONENTS)
ERREXIT1(cinfo->emethods, "Cannot quantize more than %d color components",
MAX_COMPONENTS);
/* Make sure colormap indexes can be represented by JSAMPLEs */
if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
ERREXIT1(cinfo->emethods, "Cannot request more than %d quantized colors",
MAXJSAMPLE+1);
/* Select number of colors for each component */
total_colors = select_ncolors(cinfo, Ncolors);
/* Report selected color counts */
if (cinfo->color_out_comps == 3)
TRACEMS4(cinfo->emethods, 1, "Quantizing to %d = %d*%d*%d colors",
total_colors, Ncolors[0], Ncolors[1], Ncolors[2]);
else
TRACEMS1(cinfo->emethods, 1, "Quantizing to %d colors", total_colors);
/* Allocate and fill in the colormap and color index. */
/* The colors are ordered in the map in standard row-major order, */
/* i.e. rightmost (highest-indexed) color changes most rapidly. */
colormap = (*cinfo->emethods->alloc_small_sarray)
((long) total_colors, (long) cinfo->color_out_comps);
colorindex = (*cinfo->emethods->alloc_small_sarray)
((long) (MAXJSAMPLE+1), (long) cinfo->color_out_comps);
/* 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->color_out_comps; i++) {
/* fill in colormap entries for i'th color component */
nci = 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 */
/* fill in colorindex entries for i'th color component */
/* in loop, val = index of current output value, */
/* and k = largest j that maps to current val */
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 */
colorindex[i][j] = (JSAMPLE) (val * blksize);
}
}
/* Pass the colormap to the output module. */
/* NB: the output module may continue to use the colormap until shutdown. */
cinfo->colormap = colormap;
cinfo->actual_number_of_colors = total_colors;
(*cinfo->methods->put_color_map) (cinfo, total_colors, colormap);
/* Allocate workspace to hold one row of color-converted data */
input_buffer = (*cinfo->emethods->alloc_small_sarray)
(cinfo->image_width, (long) cinfo->color_out_comps);
/* Allocate Floyd-Steinberg workspace if necessary */
if (cinfo->use_dithering) {
size_t arraysize = (size_t) ((cinfo->image_width + 2L) * SIZEOF(FSERROR));
for (i = 0; i < cinfo->color_out_comps; i++) {
fserrors[i] = (FSERRPTR) (*cinfo->emethods->alloc_medium) (arraysize);
/* Initialize the propagated errors to zero. */
jzero_far((void FAR *) fserrors[i], arraysize);
}
on_odd_row = FALSE;
}
}
/*
* Subroutines for color conversion methods.
*/
LOCAL void
do_color_conversion (decompress_info_ptr cinfo, JSAMPIMAGE input_data, int row)
/* Convert the indicated row of the input data into output colorspace */
/* in input_buffer. This requires a little trickery since color_convert */
/* expects to deal with 3-D arrays; fortunately we can fake it out */
/* at fairly low cost. */
{
short ci;
JSAMPARRAY input_hack[MAX_COMPONENTS];
JSAMPARRAY output_hack[MAX_COMPONENTS];
/* create JSAMPIMAGE pointing at specified row of input_data */
for (ci = 0; ci < cinfo->num_components; ci++)
input_hack[ci] = input_data[ci] + row;
/* Create JSAMPIMAGE pointing at input_buffer */
for (ci = 0; ci < cinfo->color_out_comps; ci++)
output_hack[ci] = &(input_buffer[ci]);
(*cinfo->methods->color_convert) (cinfo, 1, cinfo->image_width,
input_hack, output_hack);
}
/*
* Map some rows of pixels to the output colormapped representation.
*/
METHODDEF void
color_quantize (decompress_info_ptr cinfo, int num_rows,
JSAMPIMAGE input_data, JSAMPARRAY output_data)
/* General case, no dithering */
{
register int pixcode, ci;
register JSAMPROW ptrout;
register long col;
int row;
long width = cinfo->image_width;
register int nc = cinfo->color_out_comps;
for (row = 0; row < num_rows; row++) {
do_color_conversion(cinfo, input_data, row);
ptrout = output_data[row];
for (col = 0; col < width; col++) {
pixcode = 0;
for (ci = 0; ci < nc; ci++) {
pixcode += GETJSAMPLE(colorindex[ci]
[GETJSAMPLE(input_buffer[ci][col])]);
}
*ptrout++ = (JSAMPLE) pixcode;
}
}
}
METHODDEF void
color_quantize3 (decompress_info_ptr cinfo, int num_rows,
JSAMPIMAGE input_data, JSAMPARRAY output_data)
/* Fast path for color_out_comps==3, no dithering */
{
register int pixcode;
register JSAMPROW ptr0, ptr1, ptr2, ptrout;
register long col;
int row;
JSAMPROW colorindex0 = colorindex[0];
JSAMPROW colorindex1 = colorindex[1];
JSAMPROW colorindex2 = colorindex[2];
long width = cinfo->image_width;
for (row = 0; row < num_rows; row++) {
do_color_conversion(cinfo, input_data, row);
ptr0 = input_buffer[0];
ptr1 = input_buffer[1];
ptr2 = input_buffer[2];
ptrout = output_data[row];
for (col = width; col > 0; col--) {
pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptr0++)]);
pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptr1++)]);
pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptr2++)]);
*ptrout++ = (JSAMPLE) pixcode;
}
}
}
METHODDEF void
color_quantize_dither (decompress_info_ptr cinfo, int num_rows,
JSAMPIMAGE input_data, JSAMPARRAY output_data)
/* General case, with Floyd-Steinberg dithering */
{
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 dir; /* 1 for left-to-right, -1 for right-to-left */
int ci;
int nc = cinfo->color_out_comps;
int row;
long col_counter;
long width = cinfo->image_width;
JSAMPLE *range_limit = cinfo->sample_range_limit;
SHIFT_TEMPS
for (row = 0; row < num_rows; row++) {
do_color_conversion(cinfo, input_data, row);
/* Initialize output values to 0 so can process components separately */
jzero_far((void FAR *) output_data[row],
(size_t) (width * SIZEOF(JSAMPLE)));
for (ci = 0; ci < nc; ci++) {
input_ptr = input_buffer[ci];
output_ptr = output_data[row];
if (on_odd_row) {
/* work right to left in this row */
input_ptr += width - 1; /* so point to rightmost pixel */
output_ptr += width - 1;
dir = -1;
errorptr = fserrors[ci] + (width+1); /* point to entry after last column */
} else {
/* work left to right in this row */
dir = 1;
errorptr = fserrors[ci]; /* point to entry before first real column */
}
colorindex_ci = colorindex[ci];
colormap_ci = 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_counter = width; col_counter > 0; col_counter--) {
/* 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 += dir; /* 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 */
}
on_odd_row = (on_odd_row ? FALSE : TRUE);
}
}
/*
* Finish up at the end of the file.
*/
METHODDEF void
color_quant_term (decompress_info_ptr cinfo)
{
/* no work (we let free_all release the workspace) */
/* Note that we *mustn't* free the colormap before free_all, */
/* since output module may use it! */
}
/*
* Prescan some rows of pixels.
* Not used in one-pass case.
*/
METHODDEF void
color_quant_prescan (decompress_info_ptr cinfo, int num_rows,
JSAMPIMAGE image_data, JSAMPARRAY workspace)
{
ERREXIT(cinfo->emethods, "Should not get here!");
}
/*
* Do two-pass quantization.
* Not used in one-pass case.
*/
METHODDEF void
color_quant_doit (decompress_info_ptr cinfo, quantize_caller_ptr source_method)
{
ERREXIT(cinfo->emethods, "Should not get here!");
}
/*
* The method selection routine for 1-pass color quantization.
*/
GLOBAL void
jsel1quantize (decompress_info_ptr cinfo)
{
if (! cinfo->two_pass_quantize) {
cinfo->methods->color_quant_init = color_quant_init;
if (cinfo->use_dithering) {
cinfo->methods->color_quantize = color_quantize_dither;
} else {
if (cinfo->color_out_comps == 3)
cinfo->methods->color_quantize = color_quantize3;
else
cinfo->methods->color_quantize = color_quantize;
}
cinfo->methods->color_quant_prescan = color_quant_prescan;
cinfo->methods->color_quant_doit = color_quant_doit;
cinfo->methods->color_quant_term = color_quant_term;
}
}
#endif /* QUANT_1PASS_SUPPORTED */
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