From ff8c2c41030289b4a6ea6d547c91c90bc8484f26 Mon Sep 17 00:00:00 2001
From: Vittorio Giovara <vittorio.giovara@gmail.com>
Date: Tue, 19 Jan 2016 23:12:39 +0100
Subject: [PATCH] yuv2rgb: Document the color space coefficients
Based on the original documentation found in mpeg2dec (1995).
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
---
libswscale/yuv2rgb.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/libswscale/yuv2rgb.c b/libswscale/yuv2rgb.c
index e81f3f6f313..3671fe342fc 100644
--- a/libswscale/yuv2rgb.c
+++ b/libswscale/yuv2rgb.c
@@ -35,6 +35,17 @@
#include "swscale_internal.h"
#include "libavutil/pixdesc.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] = {
{ 117504, 138453, 13954, 34903 }, /* no sequence_display_extension */
{ 117504, 138453, 13954, 34903 }, /* ITU-R Rec. 709 (1990) */
--
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