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/*
* jdcolor.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 output colorspace conversion routines.
* These routines are invoked via the methods color_convert
* and colorout_init/term.
*/
#include "jinclude.h"
/**************** YCbCr -> RGB 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
* R = Y + 1.40200 * Cr
* G = Y - 0.34414 * Cb - 0.71414 * Cr
* B = Y + 1.77200 * Cb
* where Cb and Cr represent the incoming values less 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.
* Notice that Y, being an integral input, does not contribute any fraction
* so it need not participate in the rounding.
*
* For even more speed, we avoid doing any multiplications in the inner loop
* by precalculating the constants times Cb and Cr 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 Cr=>R and Cb=>B values can be rounded to integers in advance; the
* values for the G calculation are left scaled up, since we must add them
* together before rounding.
*/
#ifdef SIXTEEN_BIT_SAMPLES
#define SCALEBITS 14 /* avoid overflow */
#else
#define SCALEBITS 16 /* speedier right-shift on some machines */
#endif
#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
static int * Cr_r_tab; /* => table for Cr to R conversion */
static int * Cb_b_tab; /* => table for Cb to B conversion */
static INT32 * Cr_g_tab; /* => table for Cr to G conversion */
static INT32 * Cb_g_tab; /* => table for Cb to G conversion */
/*
* Initialize for colorspace conversion.
*/
METHODDEF void
ycc_rgb_init (decompress_info_ptr cinfo)
{
INT32 i, x2;
SHIFT_TEMPS
Cr_r_tab = (int *) (*cinfo->emethods->alloc_small)
((MAXJSAMPLE+1) * SIZEOF(int));
Cb_b_tab = (int *) (*cinfo->emethods->alloc_small)
((MAXJSAMPLE+1) * SIZEOF(int));
Cr_g_tab = (INT32 *) (*cinfo->emethods->alloc_small)
((MAXJSAMPLE+1) * SIZEOF(INT32));
Cb_g_tab = (INT32 *) (*cinfo->emethods->alloc_small)
((MAXJSAMPLE+1) * SIZEOF(INT32));
for (i = 0; i <= MAXJSAMPLE; i++) {
/* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
/* The Cb or Cr value we are thinking of is x = i - MAXJSAMPLE/2 */
x2 = 2*i - MAXJSAMPLE; /* twice x */
/* Cr=>R value is nearest int to 1.40200 * x */
Cr_r_tab[i] = (int)
RIGHT_SHIFT(FIX(1.40200/2) * x2 + ONE_HALF, SCALEBITS);
/* Cb=>B value is nearest int to 1.77200 * x */
Cb_b_tab[i] = (int)
RIGHT_SHIFT(FIX(1.77200/2) * x2 + ONE_HALF, SCALEBITS);
/* Cr=>G value is scaled-up -0.71414 * x */
Cr_g_tab[i] = (- FIX(0.71414/2)) * x2;
/* Cb=>G value is scaled-up -0.34414 * x */
/* We also add in ONE_HALF so that need not do it in inner loop */
Cb_g_tab[i] = (- FIX(0.34414/2)) * x2 + ONE_HALF;
}
}
/*
* Convert some rows of samples to the output colorspace.
*/
METHODDEF void
ycc_rgb_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
JSAMPIMAGE input_data, JSAMPIMAGE output_data)
{
#ifdef SIXTEEN_BIT_SAMPLES
register INT32 y;
register UINT16 cb, cr;
#else
register int y, cb, cr;
#endif
register JSAMPROW inptr0, inptr1, inptr2;
register JSAMPROW outptr0, outptr1, outptr2;
register long col;
/* copy these pointers into registers if possible */
register JSAMPLE * range_limit = cinfo->sample_range_limit;
register int * Crrtab = Cr_r_tab;
register int * Cbbtab = Cb_b_tab;
register INT32 * Crgtab = Cr_g_tab;
register INT32 * Cbgtab = Cb_g_tab;
int row;
SHIFT_TEMPS
for (row = 0; row < num_rows; row++) {
inptr0 = input_data[0][row];
inptr1 = input_data[1][row];
inptr2 = input_data[2][row];
outptr0 = output_data[0][row];
outptr1 = output_data[1][row];
outptr2 = output_data[2][row];
for (col = 0; col < num_cols; col++) {
y = GETJSAMPLE(inptr0[col]);
cb = GETJSAMPLE(inptr1[col]);
cr = GETJSAMPLE(inptr2[col]);
/* Note: if the inputs were computed directly from RGB values,
* range-limiting would be unnecessary here; but due to possible
* noise in the DCT/IDCT phase, we do need to apply range limits.
*/
outptr0[col] = range_limit[y + Crrtab[cr]]; /* red */
outptr1[col] = range_limit[y + /* green */
((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
SCALEBITS))];
outptr2[col] = range_limit[y + Cbbtab[cb]]; /* blue */
}
}
}
/*
* Finish up at the end of the file.
*/
METHODDEF void
ycc_rgb_term (decompress_info_ptr cinfo)
{
/* no work (we let free_all release the workspace) */
}
/**************** Cases other than YCbCr -> RGB **************/
/*
* Initialize for colorspace conversion.
*/
METHODDEF void
null_init (decompress_info_ptr cinfo)
/* colorout_init for cases where no setup is needed */
{
/* no work needed */
}
/*
* Color conversion for no colorspace change: just copy the data.
*/
METHODDEF void
null_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
JSAMPIMAGE input_data, JSAMPIMAGE output_data)
{
short ci;
for (ci = 0; ci < cinfo->num_components; ci++) {
jcopy_sample_rows(input_data[ci], 0, output_data[ci], 0,
num_rows, num_cols);
}
}
/*
* Color conversion for grayscale: just copy the data.
* This also works for YCbCr/YIQ -> grayscale conversion, in which
* we just copy the Y (luminance) component and ignore chrominance.
*/
METHODDEF void
grayscale_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
JSAMPIMAGE input_data, JSAMPIMAGE output_data)
{
jcopy_sample_rows(input_data[0], 0, output_data[0], 0,
num_rows, num_cols);
}
/*
* Finish up at the end of the file.
*/
METHODDEF void
null_term (decompress_info_ptr cinfo)
/* colorout_term for cases where no teardown is needed */
{
/* no work needed */
}
/*
* The method selection routine for output colorspace conversion.
*/
GLOBAL void
jseldcolor (decompress_info_ptr cinfo)
{
int ci;
/* Make sure num_components agrees with jpeg_color_space */
switch (cinfo->jpeg_color_space) {
case CS_GRAYSCALE:
if (cinfo->num_components != 1)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
break;
case CS_RGB:
case CS_YCbCr:
case CS_YIQ:
if (cinfo->num_components != 3)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
break;
case CS_CMYK:
if (cinfo->num_components != 4)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
break;
default:
ERREXIT(cinfo->emethods, "Unsupported JPEG colorspace");
break;
}
/* Set color_out_comps and conversion method based on requested space. */
/* Also clear the component_needed flags for any unused components, */
/* so that earlier pipeline stages can avoid useless computation. */
switch (cinfo->out_color_space) {
case CS_GRAYSCALE:
cinfo->color_out_comps = 1;
if (cinfo->jpeg_color_space == CS_GRAYSCALE ||
cinfo->jpeg_color_space == CS_YCbCr ||
cinfo->jpeg_color_space == CS_YIQ) {
cinfo->methods->color_convert = grayscale_convert;
cinfo->methods->colorout_init = null_init;
cinfo->methods->colorout_term = null_term;
/* For color->grayscale conversion, only the Y (0) component is needed */
for (ci = 1; ci < cinfo->num_components; ci++)
cinfo->cur_comp_info[ci]->component_needed = FALSE;
} else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
case CS_RGB:
cinfo->color_out_comps = 3;
if (cinfo->jpeg_color_space == CS_YCbCr) {
cinfo->methods->color_convert = ycc_rgb_convert;
cinfo->methods->colorout_init = ycc_rgb_init;
cinfo->methods->colorout_term = ycc_rgb_term;
} else if (cinfo->jpeg_color_space == CS_RGB) {
cinfo->methods->color_convert = null_convert;
cinfo->methods->colorout_init = null_init;
cinfo->methods->colorout_term = null_term;
} else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
default:
/* Permit null conversion from CMYK or YCbCr to same output space */
if (cinfo->out_color_space == cinfo->jpeg_color_space) {
cinfo->color_out_comps = cinfo->num_components;
cinfo->methods->color_convert = null_convert;
cinfo->methods->colorout_init = null_init;
cinfo->methods->colorout_term = null_term;
} else /* unsupported non-null conversion */
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
}
if (cinfo->quantize_colors)
cinfo->final_out_comps = 1; /* single colormapped output component */
else
cinfo->final_out_comps = cinfo->color_out_comps;
}
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