* jccolor.c
*
* Copyright (C) 1991-1996, Thomas G. Lane.
- * Modified 2011-2012 by Guido Vollbeding.
+ * Modified 2011-2013 by Guido Vollbeding.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
/**************** 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 + CENTERJSAMPLE
- * Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + CENTERJSAMPLE
- * (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
+ * YCbCr is defined per Recommendation ITU-R BT.601-7 (03/2011),
+ * previously known as Recommendation CCIR 601-1, except that Cb and Cr
+ * are normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
+ * sRGB (standard RGB color space) is defined per IEC 61966-2-1:1999.
+ * sYCC (standard luma-chroma-chroma color space with extended gamut)
+ * is defined per IEC 61966-2-1:1999 Amendment A1:2003 Annex F.
+ * bg-sRGB and bg-sYCC (big gamut standard color spaces)
+ * are defined per IEC 61966-2-1:1999 Amendment A1:2003 Annex G.
+ * Note that the derived conversion coefficients given in some of these
+ * documents are imprecise. The general conversion equations are
+ * Y = Kr * R + (1 - Kr - Kb) * G + Kb * B
+ * Cb = 0.5 * (B - Y) / (1 - Kb)
+ * Cr = 0.5 * (R - Y) / (1 - Kr)
+ * With Kr = 0.299 and Kb = 0.114 (derived according to SMPTE RP 177-1993
+ * from the 1953 FCC NTSC primaries and CIE Illuminant C),
+ * the conversion equations to be implemented are therefore
+ * Y = 0.299 * R + 0.587 * G + 0.114 * B
+ * Cb = -0.168735892 * R - 0.331264108 * G + 0.5 * B + CENTERJSAMPLE
+ * Cr = 0.5 * R - 0.418687589 * G - 0.081312411 * B + CENTERJSAMPLE
* Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
* rather than CENTERJSAMPLE, for Cb and Cr. This gave equal positive and
* negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
* 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.
+ * for 9-bit to 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 CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
* in the tables to save adding them separately in the inner loop.
*/
(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+R_Y_OFF] = FIX(0.299) * i;
+ rgb_ycc_tab[i+G_Y_OFF] = FIX(0.587) * i;
+ rgb_ycc_tab[i+B_Y_OFF] = FIX(0.114) * i + ONE_HALF;
+ rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.168735892)) * i;
+ rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.331264108)) * i;
/* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
* This ensures that the maximum output will round to MAXJSAMPLE
* not MAXJSAMPLE+1, and thus that we don't have to range-limit.
*/
- rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
+ rgb_ycc_tab[i+B_CB_OFF] = FIX(0.5) * i + CBCR_OFFSET + ONE_HALF-1;
/* B=>Cb and R=>Cr tables are the same
- rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
+ rgb_ycc_tab[i+R_CR_OFF] = FIX(0.5) * i + CBCR_OFFSET + ONE_HALF-1;
*/
- rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
- rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
+ rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.418687589)) * i;
+ rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.081312411)) * i;
}
}
* Convert some rows of samples to the JPEG colorspace.
* [R,G,B] to [R-G,G,B-G] conversion with modulo calculation
* (forward reversible color transform).
+ * This can be seen as an adaption of the general RGB->YCbCr
+ * conversion equation with Kr = Kb = 0, while replacing the
+ * normalization by modulo calculation.
*/
METHODDEF(void)
/*
* Convert some rows of samples to the JPEG colorspace.
* This version handles grayscale output with no conversion.
- * The source can be either plain grayscale or YCbCr (since Y == gray).
+ * The source can be either plain grayscale or YCC (since Y == gray).
*/
METHODDEF(void)
break;
case JCS_RGB:
+ case JCS_BG_RGB:
if (cinfo->input_components != RGB_PIXELSIZE)
ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
break;
case JCS_YCbCr:
+ case JCS_BG_YCC:
if (cinfo->input_components != 3)
ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
break;
break;
}
- /* Support color transform only for RGB colorspace */
- if (cinfo->color_transform && cinfo->jpeg_color_space != JCS_RGB)
+ /* Support color transform only for RGB colorspaces */
+ if (cinfo->color_transform &&
+ cinfo->jpeg_color_space != JCS_RGB &&
+ cinfo->jpeg_color_space != JCS_BG_RGB)
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
/* Check num_components, set conversion method based on requested space */
case JCS_GRAYSCALE:
if (cinfo->num_components != 1)
ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
- if (cinfo->in_color_space == JCS_GRAYSCALE ||
- cinfo->in_color_space == JCS_YCbCr)
+ switch (cinfo->in_color_space) {
+ case JCS_GRAYSCALE:
+ case JCS_YCbCr:
+ case JCS_BG_YCC:
cconvert->pub.color_convert = grayscale_convert;
- else if (cinfo->in_color_space == JCS_RGB) {
+ break;
+ case JCS_RGB:
cconvert->pub.start_pass = rgb_ycc_start;
cconvert->pub.color_convert = rgb_gray_convert;
- } else
+ break;
+ default:
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
+ }
break;
case JCS_RGB:
+ case JCS_BG_RGB:
if (cinfo->num_components != 3)
ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
- if (cinfo->in_color_space == JCS_RGB) {
+ if (cinfo->in_color_space == cinfo->jpeg_color_space) {
switch (cinfo->color_transform) {
case JCT_NONE:
cconvert->pub.color_convert = rgb_convert;
break;
default:
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
- break;
}
} else
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
case JCS_YCbCr:
if (cinfo->num_components != 3)
ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
- if (cinfo->in_color_space == JCS_RGB) {
+ switch (cinfo->in_color_space) {
+ case JCS_RGB:
cconvert->pub.start_pass = rgb_ycc_start;
cconvert->pub.color_convert = rgb_ycc_convert;
- } else if (cinfo->in_color_space == JCS_YCbCr)
+ break;
+ case JCS_YCbCr:
cconvert->pub.color_convert = null_convert;
- else
+ break;
+ default:
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
+ }
+ break;
+
+ case JCS_BG_YCC:
+ if (cinfo->num_components != 3)
+ ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
+ switch (cinfo->in_color_space) {
+ case JCS_RGB:
+ /* For conversion from normal RGB input to BG_YCC representation,
+ * the Cb/Cr values are first computed as usual, and then
+ * quantized further after DCT processing by a factor of
+ * 2 in reference to the nominal quantization factor.
+ */
+ /* need quantization scale by factor of 2 after DCT */
+ cinfo->comp_info[1].component_needed = TRUE;
+ cinfo->comp_info[2].component_needed = TRUE;
+ /* compute normal YCC first */
+ cconvert->pub.start_pass = rgb_ycc_start;
+ cconvert->pub.color_convert = rgb_ycc_convert;
+ break;
+ case JCS_YCbCr:
+ /* need quantization scale by factor of 2 after DCT */
+ cinfo->comp_info[1].component_needed = TRUE;
+ cinfo->comp_info[2].component_needed = TRUE;
+ /*FALLTHROUGH*/
+ case JCS_BG_YCC:
+ /* Pass through for BG_YCC input */
+ cconvert->pub.color_convert = null_convert;
+ break;
+ default:
+ ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
+ }
break;
case JCS_CMYK:
case JCS_YCCK:
if (cinfo->num_components != 4)
ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
- if (cinfo->in_color_space == JCS_CMYK) {
+ switch (cinfo->in_color_space) {
+ case JCS_CMYK:
cconvert->pub.start_pass = rgb_ycc_start;
cconvert->pub.color_convert = cmyk_ycck_convert;
- } else if (cinfo->in_color_space == JCS_YCCK)
+ break;
+ case JCS_YCCK:
cconvert->pub.color_convert = null_convert;
- else
+ break;
+ default:
ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
+ }
break;
default: /* allow null conversion of JCS_UNKNOWN */
projects / reactos.git / blobdiff