295 lines
8.9 KiB
C
295 lines
8.9 KiB
C
/*
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* jdcolor.c
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*
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* Copyright (C) 1991, 1992, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains output colorspace conversion routines.
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* These routines are invoked via the methods color_convert
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* and colorout_init/term.
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*/
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#include "jinclude.h"
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/**************** YCbCr -> RGB conversion: most common case **************/
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/*
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* YCbCr is defined per CCIR 601-1, except that Cb and Cr are
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* normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
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* The conversion equations to be implemented are therefore
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* R = Y + 1.40200 * Cr
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* G = Y - 0.34414 * Cb - 0.71414 * Cr
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* B = Y + 1.77200 * Cb
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* where Cb and Cr represent the incoming values less MAXJSAMPLE/2.
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* (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
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*
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* To avoid floating-point arithmetic, we represent the fractional constants
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* as integers scaled up by 2^16 (about 4 digits precision); we have to divide
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* the products by 2^16, with appropriate rounding, to get the correct answer.
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* Notice that Y, being an integral input, does not contribute any fraction
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* so it need not participate in the rounding.
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*
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* For even more speed, we avoid doing any multiplications in the inner loop
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* by precalculating the constants times Cb and Cr for all possible values.
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* For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
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* for 12-bit samples it is still acceptable. It's not very reasonable for
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* 16-bit samples, but if you want lossless storage you shouldn't be changing
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* colorspace anyway.
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* The Cr=>R and Cb=>B values can be rounded to integers in advance; the
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* values for the G calculation are left scaled up, since we must add them
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* together before rounding.
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*/
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#ifdef SIXTEEN_BIT_SAMPLES
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#define SCALEBITS 14 /* avoid overflow */
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#else
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#define SCALEBITS 16 /* speedier right-shift on some machines */
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#endif
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#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
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#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
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static int * Cr_r_tab; /* => table for Cr to R conversion */
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static int * Cb_b_tab; /* => table for Cb to B conversion */
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static INT32 * Cr_g_tab; /* => table for Cr to G conversion */
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static INT32 * Cb_g_tab; /* => table for Cb to G conversion */
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/*
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* Initialize for colorspace conversion.
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*/
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METHODDEF void
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ycc_rgb_init (decompress_info_ptr cinfo)
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{
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INT32 i, x2;
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SHIFT_TEMPS
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Cr_r_tab = (int *) (*cinfo->emethods->alloc_small)
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((MAXJSAMPLE+1) * SIZEOF(int));
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Cb_b_tab = (int *) (*cinfo->emethods->alloc_small)
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((MAXJSAMPLE+1) * SIZEOF(int));
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Cr_g_tab = (INT32 *) (*cinfo->emethods->alloc_small)
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((MAXJSAMPLE+1) * SIZEOF(INT32));
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Cb_g_tab = (INT32 *) (*cinfo->emethods->alloc_small)
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((MAXJSAMPLE+1) * SIZEOF(INT32));
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for (i = 0; i <= MAXJSAMPLE; i++) {
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/* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
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/* The Cb or Cr value we are thinking of is x = i - MAXJSAMPLE/2 */
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x2 = 2*i - MAXJSAMPLE; /* twice x */
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/* Cr=>R value is nearest int to 1.40200 * x */
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Cr_r_tab[i] = (int)
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RIGHT_SHIFT(FIX(1.40200/2) * x2 + ONE_HALF, SCALEBITS);
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/* Cb=>B value is nearest int to 1.77200 * x */
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Cb_b_tab[i] = (int)
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RIGHT_SHIFT(FIX(1.77200/2) * x2 + ONE_HALF, SCALEBITS);
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/* Cr=>G value is scaled-up -0.71414 * x */
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Cr_g_tab[i] = (- FIX(0.71414/2)) * x2;
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/* Cb=>G value is scaled-up -0.34414 * x */
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/* We also add in ONE_HALF so that need not do it in inner loop */
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Cb_g_tab[i] = (- FIX(0.34414/2)) * x2 + ONE_HALF;
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}
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}
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/*
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* Convert some rows of samples to the output colorspace.
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*/
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METHODDEF void
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ycc_rgb_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
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JSAMPIMAGE input_data, JSAMPIMAGE output_data)
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{
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#ifdef SIXTEEN_BIT_SAMPLES
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register INT32 y;
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register UINT16 cb, cr;
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#else
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register int y, cb, cr;
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#endif
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register JSAMPROW inptr0, inptr1, inptr2;
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register JSAMPROW outptr0, outptr1, outptr2;
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register long col;
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/* copy these pointers into registers if possible */
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register JSAMPLE * range_limit = cinfo->sample_range_limit;
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register int * Crrtab = Cr_r_tab;
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register int * Cbbtab = Cb_b_tab;
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register INT32 * Crgtab = Cr_g_tab;
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register INT32 * Cbgtab = Cb_g_tab;
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int row;
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SHIFT_TEMPS
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for (row = 0; row < num_rows; row++) {
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inptr0 = input_data[0][row];
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inptr1 = input_data[1][row];
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inptr2 = input_data[2][row];
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outptr0 = output_data[0][row];
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outptr1 = output_data[1][row];
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outptr2 = output_data[2][row];
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for (col = 0; col < num_cols; col++) {
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y = GETJSAMPLE(inptr0[col]);
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cb = GETJSAMPLE(inptr1[col]);
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cr = GETJSAMPLE(inptr2[col]);
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/* Note: if the inputs were computed directly from RGB values,
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* range-limiting would be unnecessary here; but due to possible
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* noise in the DCT/IDCT phase, we do need to apply range limits.
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*/
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outptr0[col] = range_limit[y + Crrtab[cr]]; /* red */
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outptr1[col] = range_limit[y + /* green */
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((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
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SCALEBITS))];
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outptr2[col] = range_limit[y + Cbbtab[cb]]; /* blue */
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}
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}
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}
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/*
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* Finish up at the end of the file.
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*/
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METHODDEF void
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ycc_rgb_term (decompress_info_ptr cinfo)
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{
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/* no work (we let free_all release the workspace) */
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}
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/**************** Cases other than YCbCr -> RGB **************/
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/*
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* Initialize for colorspace conversion.
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*/
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METHODDEF void
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null_init (decompress_info_ptr cinfo)
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/* colorout_init for cases where no setup is needed */
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{
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/* no work needed */
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}
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/*
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* Color conversion for no colorspace change: just copy the data.
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*/
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METHODDEF void
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null_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
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JSAMPIMAGE input_data, JSAMPIMAGE output_data)
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{
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short ci;
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for (ci = 0; ci < cinfo->num_components; ci++) {
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jcopy_sample_rows(input_data[ci], 0, output_data[ci], 0,
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num_rows, num_cols);
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}
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}
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/*
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* Color conversion for grayscale: just copy the data.
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* This also works for YCbCr/YIQ -> grayscale conversion, in which
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* we just copy the Y (luminance) component and ignore chrominance.
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*/
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METHODDEF void
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grayscale_convert (decompress_info_ptr cinfo, int num_rows, long num_cols,
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JSAMPIMAGE input_data, JSAMPIMAGE output_data)
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{
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jcopy_sample_rows(input_data[0], 0, output_data[0], 0,
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num_rows, num_cols);
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}
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/*
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* Finish up at the end of the file.
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*/
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METHODDEF void
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null_term (decompress_info_ptr cinfo)
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/* colorout_term for cases where no teardown is needed */
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{
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/* no work needed */
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}
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/*
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* The method selection routine for output colorspace conversion.
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*/
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GLOBAL void
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jseldcolor (decompress_info_ptr cinfo)
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{
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/* Make sure num_components agrees with jpeg_color_space */
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switch (cinfo->jpeg_color_space) {
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case CS_GRAYSCALE:
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if (cinfo->num_components != 1)
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ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
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break;
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case CS_RGB:
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case CS_YCbCr:
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case CS_YIQ:
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if (cinfo->num_components != 3)
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ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
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break;
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case CS_CMYK:
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if (cinfo->num_components != 4)
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ERREXIT(cinfo->emethods, "Bogus JPEG colorspace");
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break;
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default:
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ERREXIT(cinfo->emethods, "Unsupported JPEG colorspace");
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break;
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}
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/* Set color_out_comps and conversion method based on requested space */
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switch (cinfo->out_color_space) {
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case CS_GRAYSCALE:
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cinfo->color_out_comps = 1;
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if (cinfo->jpeg_color_space == CS_GRAYSCALE ||
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cinfo->jpeg_color_space == CS_YCbCr ||
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cinfo->jpeg_color_space == CS_YIQ) {
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cinfo->methods->color_convert = grayscale_convert;
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cinfo->methods->colorout_init = null_init;
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cinfo->methods->colorout_term = null_term;
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} else
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ERREXIT(cinfo->emethods, "Unsupported color conversion request");
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break;
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case CS_RGB:
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cinfo->color_out_comps = 3;
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if (cinfo->jpeg_color_space == CS_YCbCr) {
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cinfo->methods->color_convert = ycc_rgb_convert;
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cinfo->methods->colorout_init = ycc_rgb_init;
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cinfo->methods->colorout_term = ycc_rgb_term;
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} else if (cinfo->jpeg_color_space == CS_RGB) {
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cinfo->methods->color_convert = null_convert;
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cinfo->methods->colorout_init = null_init;
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cinfo->methods->colorout_term = null_term;
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} else
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ERREXIT(cinfo->emethods, "Unsupported color conversion request");
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break;
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default:
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/* Permit null conversion from CMYK or YCbCr to same output space */
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if (cinfo->out_color_space == cinfo->jpeg_color_space) {
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cinfo->color_out_comps = cinfo->num_components;
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cinfo->methods->color_convert = null_convert;
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cinfo->methods->colorout_init = null_init;
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cinfo->methods->colorout_term = null_term;
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} else /* unsupported non-null conversion */
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ERREXIT(cinfo->emethods, "Unsupported color conversion request");
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break;
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}
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if (cinfo->quantize_colors)
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cinfo->final_out_comps = 1; /* single colormapped output component */
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else
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cinfo->final_out_comps = cinfo->color_out_comps;
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}
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