/*
* jquant2.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 2-pass color quantization (color mapping) routines.
* These routines provide selection of a custom color map for an image,
* followed by mapping of the image to that color map, with optional
* Floyd-Steinberg dithering.
* It is also possible to use just the second pass to map to an arbitrary
* externally-given color map.
*
* Note: ordered dithering is not supported, since there isn't any fast
* way to compute intercolor distances; it's unclear that ordered dither's
* fundamental assumptions even hold with an irregularly spaced color map.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#ifdef QUANT_2PASS_SUPPORTED
/*
* This module implements the well-known Heckbert paradigm for color
* quantization. Most of the ideas used here can be traced back to
* Heckbert's seminal paper
* Heckbert, Paul. "Color Image Quantization for Frame Buffer Display",
* Proc. SIGGRAPH '82, Computer Graphics v.16 #3 (July 1982), pp 297-304.
*
* In the first pass over the image, we accumulate a histogram showing the
* usage count of each possible color. To keep the histogram to a reasonable
* size, we reduce the precision of the input; typical practice is to retain
* 5 or 6 bits per color, so that 8 or 4 different input values are counted
* in the same histogram cell.
*
* Next, the color-selection step begins with a box representing the whole
* color space, and repeatedly splits the "largest" remaining box until we
* have as many boxes as desired colors. Then the mean color in each
* remaining box becomes one of the possible output colors.
*
* The second pass over the image maps each input pixel to the closest output
* color (optionally after applying a Floyd-Steinberg dithering correction).
* This mapping is logically trivial, but making it go fast enough requires
* considerable care.
*
* Heckbert-style quantizers vary a good deal in their policies for choosing
* the "largest" box and deciding where to cut it. The particular policies
* used here have proved out well in experimental comparisons, but better ones
* may yet be found.
*
* In earlier versions of the IJG code, this module quantized in YCbCr color
* space, processing the raw upsampled data without a color conversion step.
* This allowed the color conversion math to be done only once per colormap
* entry, not once per pixel. However, that optimization precluded other
* useful optimizations (such as merging color conversion with upsampling)
* and it also interfered with desired capabilities such as quantizing to an
* externally-supplied colormap. We have therefore abandoned that approach.
* The present code works in the post-conversion color space, typically RGB.
*
* To improve the visual quality of the results, we actually work in scaled
* RGB space, giving G distances more weight than R, and R in turn more than
* B. To do everything in integer math, we must use integer scale factors.
* The 2/3/1 scale factors used here correspond loosely to the relative
* weights of the colors in the NTSC grayscale equation.
* If you want to use this code to quantize a non-RGB color space, you'll
* probably need to change these scale factors.
*/
#define R_SCALE 2 /* scale R distances by this much */
#define G_SCALE 3 /* scale G distances by this much */
#define B_SCALE 1 /* and B by this much */
/* Relabel R/G/B as components 0/1/2, respecting the RGB ordering defined
* in jmorecfg.h. As the code stands, it will do the right thing for R,G,B
* and B,G,R orders. If you define some other weird order in jmorecfg.h,
* you'll get compile errors until you extend this logic. In that case
* you'll probably want to tweak the histogram sizes too.
*/
#if RGB_RED == 0
#define C0_SCALE R_SCALE
#endif
#if RGB_BLUE == 0
#define C0_SCALE B_SCALE
#endif
#if RGB_GREEN == 1
#define C1_SCALE G_SCALE
#endif
#if RGB_RED == 2
#define C2_SCALE R_SCALE
#endif
#if RGB_BLUE == 2
#define C2_SCALE B_SCALE
#endif
/*
* First we have the histogram data structure and routines for creating it.
*
* The number of bits of precision can be adjusted by changing these symbols.
* We recommend keeping 6 bits for G and 5 each for R and B.
* If you have plenty of memory and cycles, 6 bits all around gives marginally
* better results; if you are short of memory, 5 bits all around will save
* some space but degrade the results.
* To maintain a fully accurate histogram, we'd need to allocate a "long"
* (preferably unsigned long) for each cell. In practice this is overkill;
* we can get by with 16 bits per cell. Few of the cell counts will overflow,
* and clamping those that do overflow to the maximum value will give close-
* enough results. This reduces the recommended histogram size from 256Kb
* to 128Kb, which is a useful savings on PC-class machines.
* (In the second pass the histogram space is re-used for pixel mapping data;
* in that capacity, each cell must be able to store zero to the number of
* desired colors. 16 bits/cell is plenty for that too.)
* Since the JPEG code is intended to run in small memory model on 80x86
* machines, we can't just allocate the histogram in one chunk. Instead
* of a true 3-D array, we use a row of pointers to 2-D arrays. Each
* pointer corresponds to a C0 value (typically 2^5 = 32 pointers) and
* each 2-D array has 2^6*2^5 = 2048 or 2^6*2^6 = 4096 entries. Note that
* on 80x86 machines, the pointer row is in near memory but the actual
* arrays are in far memory (same arrangement as we use for image arrays).
*/
#define MAXNUMCOLORS (MAXJSAMPLE+1) /* maximum size of colormap */
/* These will do the right thing for either R,G,B or B,G,R color order,
* but you may not like the results for other color orders.
*/
#define HIST_C0_BITS 5 /* bits of precision in R/B histogram */
#define HIST_C1_BITS 6 /* bits of precision in G histogram */
#define HIST_C2_BITS 5 /* bits of precision in B/R histogram */
/* Number of elements along histogram axes. */
#define HIST_C0_ELEMS (1<<HIST_C0_BITS)
#define HIST_C1_ELEMS (1<<HIST_C1_BITS)
#define HIST_C2_ELEMS (1<<HIST_C2_BITS)
/* These are the amounts to shift an input value to get a histogram index. */
#define C0_SHIFT (BITS_IN_JSAMPLE-HIST_C0_BITS)
#define C1_SHIFT (BITS_IN_JSAMPLE-HIST_C1_BITS)
#define C2_SHIFT (BITS_IN_JSAMPLE-HIST_C2_BITS)
typedef UINT16 histcell; /* histogram cell; prefer an unsigned type */
typedef histcell FAR * histptr; /* for pointers to histogram cells */
typedef histcell hist1d[HIST_C2_ELEMS]; /* typedefs for the array */
typedef hist1d FAR * hist2d; /* type for the 2nd-level pointers */
typedef hist2d * hist3d; /* type for top-level pointer */
/* 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 has (#columns + 2) entries; the extra entry at
* e
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bmptojpg.rar (75个子文件)
bmptojpg
jquant1.c 31KB
jctrans.c 14KB
jcmainct.c 9KB
jdct.h 7KB
jcdctmgr.c 13KB
cderror.h 5KB
jmemnobs.c 3KB
jcapimin.c 9KB
jdapimin.c 13KB
bmptojpg.ncb 41KB
jidctfst.c 13KB
jdatadst.c 5KB
jdhuff.h 8KB
jmemmgr.c 41KB
bmptojpg.opt 48KB
jfdctfst.c 8KB
jchuff.h 2KB
jfdctint.c 11KB
jdmaster.c 20KB
jdcoefct.c 25KB
jdpostct.c 10KB
jcsample.c 19KB
jcphuff.c 25KB
jdmarker.c 41KB
jquant2.c 49KB
jerror.h 13KB
jpeglib.h 46KB
jccoefct.c 16KB
jcmarker.c 17KB
bmptojpg.h 793B
jmemmac.c 10KB
jdinput.c 14KB
jidctint.c 15KB
jcomapi.c 3KB
jdsample.c 16KB
jdapistd.c 9KB
jmorecfg.h 13KB
jmemsys.h 8KB
jcinit.c 2KB
jcapistd.c 6KB
jdhuff.c 21KB
bmptojpg.dsw 524B
jdtrans.c 5KB
makefile 6KB
jddctmgr.c 8KB
jdmerge.c 14KB
jdatasrc.c 8KB
jidctflt.c 8KB
jconfig.h 9KB
jfdctflt.c 6KB
libjpeg.a 306KB
bmptojpg.dsp 3KB
jinclude.h 3KB
jccolor.c 15KB
jmemdos.c 19KB
jcprepct.c 12KB
bmptojpg.c 10KB
jdcolor.c 13KB
jerror.c 8KB
jversion.h 374B
jdphuff.c 21KB
jmemansi.c 5KB
jcparam.c 21KB
jutils.c 5KB
Debug
bmptojpg.obj 13KB
vc60.idb 33KB
vc60.pdb 60KB
bmptojpg.pdb 25KB
jpegint.h 16KB
jchuff.c 28KB
jcmaster.c 20KB
jdmainct.c 21KB
bmptojpg.plg 2KB
jmemname.c 8KB
jidctred.c 14KB
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