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yuv2rgb: Document the color space coefficients 

Based on the original documentation found in mpeg2dec (1995).

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
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Vittorio Giovara 2016-01-19 17:10:59 -05:00
parent 472d488ebc
commit e9175634ec
1 changed files with 11 additions and 0 deletions
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libswscale/yuv2rgb.c
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@ -35,6 +35,17 @@
#include "swscale.h" #include "swscale.h"
#include "swscale_internal.h" #include "swscale_internal.h"
/* Color space conversion coefficients for YCbCr -> RGB mapping.
*
* Entries are {crv, cbu, cgu, cgv}
*
* crv = (255 / 224) * 65536 * (1 - cr) / 0.5
* cbu = (255 / 224) * 65536 * (1 - cb) / 0.5
* cgu = (255 / 224) * 65536 * (cb / cg) * (1 - cb) / 0.5
* cgv = (255 / 224) * 65536 * (cr / cg) * (1 - cr) / 0.5
*
* where Y = cr * R + cg * G + cb * B and cr + cg + cb = 1.
*/
const int32_t ff_yuv2rgb_coeffs[8][4] = { const int32_t ff_yuv2rgb_coeffs[8][4] = {
{ 117504, 138453, 13954, 34903 }, /* no sequence_display_extension */ { 117504, 138453, 13954, 34903 }, /* no sequence_display_extension */
{ 117504, 138453, 13954, 34903 }, /* ITU-R Rec. 709 (1990) */ { 117504, 138453, 13954, 34903 }, /* ITU-R Rec. 709 (1990) */