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/*
* jccolor.c
*
* Copyright (C) 1991, 1992, 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.
* These routines are invoked via the methods get_sample_rows
* and colorin_init/term.
*/
#include "jinclude.h"
static JSAMPARRAY pixel_row; /* Workspace for a pixel row in input format */
/*
* Initialize for colorspace conversion.
*/
METHODDEF void
colorin_init (compress_info_ptr cinfo)
{
/* Allocate a workspace for the result of get_input_row. */
pixel_row = (*cinfo->emethods->alloc_small_sarray)
(cinfo->image_width, (long) cinfo->input_components);
}
/*
* Fetch some rows of pixels from get_input_row and convert to the
* JPEG colorspace.
*/
/*
* This version handles RGB -> YCbCr conversion.
* 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
* Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B
* where Cb and Cr must be incremented by MAXJSAMPLE/2 to create a
* nonnegative output value.
* (These numbers are derived from TIFF Appendix O, draft of 4/10/91.)
*
* To avoid floating-point arithmetic, we represent the fractional constants
* as integers scaled up by 2^14 (about 4 digits precision); we have to divide
* the products by 2^14, with appropriate rounding, to get the correct answer.
*
* For even more speed, we could avoid any multiplications in the inner loop
* by precalculating the constants times R,G,B for all possible values.
* This is not currently implemented.
*/
#define SCALEBITS 14
#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
METHODDEF void
get_rgb_ycc_rows (compress_info_ptr cinfo,
int rows_to_read, JSAMPIMAGE image_data)
{
register INT32 r, g, b;
register JSAMPROW inptr0, inptr1, inptr2;
register JSAMPROW outptr0, outptr1, outptr2;
register long col;
long width = cinfo->image_width;
int row;
for (row = 0; row < rows_to_read; row++) {
/* Read one row from the source file */
(*cinfo->methods->get_input_row) (cinfo, pixel_row);
/* Convert colorspace */
inptr0 = pixel_row[0];
inptr1 = pixel_row[1];
inptr2 = pixel_row[2];
outptr0 = image_data[0][row];
outptr1 = image_data[1][row];
outptr2 = image_data[2][row];
for (col = width; col > 0; col--) {
r = GETJSAMPLE(*inptr0++);
g = GETJSAMPLE(*inptr1++);
b = GETJSAMPLE(*inptr2++);
/* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
* must be too; we do not need an explicit range-limiting operation.
* Hence the value being shifted is never negative, and we don't
* need the general RIGHT_SHIFT macro.
*/
/* Y */
*outptr0++ = (JSAMPLE)
(( FIX(0.29900)*r + FIX(0.58700)*g + FIX(0.11400)*b
+ ONE_HALF) >> SCALEBITS);
/* Cb */
*outptr1++ = (JSAMPLE)
(((-FIX(0.16874))*r - FIX(0.33126)*g + FIX(0.50000)*b
+ ONE_HALF*(MAXJSAMPLE+1)) >> SCALEBITS);
/* Cr */
*outptr2++ = (JSAMPLE)
(( FIX(0.50000)*r - FIX(0.41869)*g - FIX(0.08131)*b
+ ONE_HALF*(MAXJSAMPLE+1)) >> SCALEBITS);
}
}
}
/*
* Fetch some rows of pixels from get_input_row and convert to the
* JPEG colorspace.
* This version handles grayscale (no conversion).
*/
METHODDEF void
get_grayscale_rows (compress_info_ptr cinfo,
int rows_to_read, JSAMPIMAGE image_data)
{
int row;
for (row = 0; row < rows_to_read; row++) {
/* Read one row from the source file */
(*cinfo->methods->get_input_row) (cinfo, pixel_row);
/* Convert colorspace (gamma mapping needed here) */
jcopy_sample_rows(pixel_row, 0, image_data[0], row,
1, cinfo->image_width);
}
}
/*
* Fetch some rows of pixels from get_input_row and convert to the
* JPEG colorspace.
* This version handles multi-component colorspaces without conversion.
*/
METHODDEF void
get_noconvert_rows (compress_info_ptr cinfo,
int rows_to_read, JSAMPIMAGE image_data)
{
int row, ci;
for (row = 0; row < rows_to_read; row++) {
/* Read one row from the source file */
(*cinfo->methods->get_input_row) (cinfo, pixel_row);
/* Convert colorspace (gamma mapping needed here) */
for (ci = 0; ci < cinfo->input_components; ci++) {
jcopy_sample_rows(pixel_row, ci, image_data[ci], row,
1, cinfo->image_width);
}
}
}
/*
* Finish up at the end of the file.
*/
METHODDEF void
colorin_term (compress_info_ptr cinfo)
{
/* no work (we let free_all release the workspace) */
}
/*
* The method selection routine for input colorspace conversion.
*/
GLOBAL void
jselccolor (compress_info_ptr cinfo)
{
/* Make sure input_components agrees with in_color_space */
switch (cinfo->in_color_space) {
case CS_GRAYSCALE:
if (cinfo->input_components != 1)
ERREXIT(cinfo->emethods, "Bogus input colorspace");
break;
case CS_RGB:
case CS_YCbCr:
case CS_YIQ:
if (cinfo->input_components != 3)
ERREXIT(cinfo->emethods, "Bogus input colorspace");
break;
case CS_CMYK:
if (cinfo->input_components != 4)
ERREXIT(cinfo->emethods, "Bogus input colorspace");
break;
default:
ERREXIT(cinfo->emethods, "Unsupported input colorspace");
break;
}
/* Check num_components, set conversion method based on requested space */
switch (cinfo->jpeg_color_space) {
case CS_GRAYSCALE:
if (cinfo->num_components != 1)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
if (cinfo->in_color_space == CS_GRAYSCALE)
cinfo->methods->get_sample_rows = get_grayscale_rows;
else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
case CS_YCbCr:
if (cinfo->num_components != 3)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
if (cinfo->in_color_space == CS_RGB)
cinfo->methods->get_sample_rows = get_rgb_ycc_rows;
else if (cinfo->in_color_space == CS_YCbCr)
cinfo->methods->get_sample_rows = get_noconvert_rows;
else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
case CS_CMYK:
if (cinfo->num_components != 4)
ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
if (cinfo->in_color_space == CS_CMYK)
cinfo->methods->get_sample_rows = get_noconvert_rows;
else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
default:
ERREXIT(cinfo->emethods, "Unsupported JPEG colorspace");
break;
}
cinfo->methods->colorin_init = colorin_init;
cinfo->methods->colorin_term = colorin_term;
}
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