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1 line
14 KiB
C
1 line
14 KiB
C
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/*
* jccolor.c
*
* Copyright (C) 1991-1994, 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 input colorspace conversion routines.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/* Private subobject */
typedef struct {
struct jpeg_color_converter pub; /* public fields */
/* Private state for RGB->YCC conversion */
INT32 * rgb_ycc_tab; /* => table for RGB to YCbCr conversion */
} my_color_converter;
typedef my_color_converter * my_cconvert_ptr;
/**************** RGB -> YCbCr conversion: most common case **************/
/*
* YCbCr is defined per CCIR 601-1, except that Cb and Cr are
* normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
* The conversion equations to be implemented are therefore
* Y = 0.29900 * R + 0.58700 * G + 0.11400 * B
* Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B + MAXJSAMPLE/2
* Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + MAXJSAMPLE/2
* (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
*
* To avoid floating-point arithmetic, we represent the fractional constants
* as integers scaled up by 2^16 (about 4 digits precision); we have to divide
* the products by 2^16, with appropriate rounding, to get the correct answer.
*
* For even more speed, we avoid doing any multiplications in the inner loop
* by precalculating the constants times R,G,B for all possible values.
* For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
* for 12-bit samples it is still acceptable. It's not very reasonable for
* 16-bit samples, but if you want lossless storage you shouldn't be changing
* colorspace anyway.
* The MAXJSAMPLE/2 offsets and the rounding fudge-factor of 0.5 are included
* in the tables to save adding them separately in the inner loop.
*/
#define SCALEBITS 16 /* speediest right-shift on some machines */
#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
/* We allocate one big table and divide it up into eight parts, instead of
* doing eight alloc_small requests. This lets us use a single table base
* address, which can be held in a register in the inner loops on many
* machines (more than can hold all eight addresses, anyway).
*/
#define R_Y_OFF 0 /* offset to R => Y section */
#define G_Y_OFF (1*(MAXJSAMPLE+1)) /* offset to G => Y section */
#define B_Y_OFF (2*(MAXJSAMPLE+1)) /* etc. */
#define R_CB_OFF (3*(MAXJSAMPLE+1))
#define G_CB_OFF (4*(MAXJSAMPLE+1))
#define B_CB_OFF (5*(MAXJSAMPLE+1))
#define R_CR_OFF B_CB_OFF /* B=>Cb, R=>Cr are the same */
#define G_CR_OFF (6*(MAXJSAMPLE+1))
#define B_CR_OFF (7*(MAXJSAMPLE+1))
#define TABLE_SIZE (8*(MAXJSAMPLE+1))
/*
* Initialize for RGB->YCC colorspace conversion.
*/
METHODDEF void
rgb_ycc_start (j_compress_ptr cinfo)
{
my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
INT32 * rgb_ycc_tab;
INT32 i;
/* Allocate and fill in the conversion tables. */
cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
(TABLE_SIZE * SIZEOF(INT32)));
for (i = 0; i <= MAXJSAMPLE; i++) {
rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i + ONE_HALF;
rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i + ONE_HALF*(MAXJSAMPLE+1);
/* B=>Cb and R=>Cr tables are the same
rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i + ONE_HALF*(MAXJSAMPLE+1);
*/
rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
}
}
/*
* Convert some rows of samples to the JPEG colorspace.
*
* Note that we change from the application's interleaved-pixel format
* to our internal noninterleaved, one-plane-per-component format.
* The input buffer is therefore three t
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