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Add details and reference about the YUV->RGB conversion

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Originated from the discussion at
   http://code.google.com/p/webp/issues/detail?id=134

Change-Id: I24384e2d2f5cf262d8632fc98303cba5e2d27224
This commit is contained in:
skal 2013-01-18 15:04:38 +01:00
parent 18e9167ea6
commit a556cb1ab4
1 changed files with 12 additions and 0 deletions
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12
src/dsp/yuv.h
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@ -14,6 +14,18 @@
// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128
// We use 16bit fixed point operations for RGB->YUV conversion.
//
// For the Y'CbCr to RGB conversion, the BT.601 specification reads:
// R = 1.164 * (Y-16) + 1.596 * (V-128)
// G = 1.164 * (Y-16) - 0.813 * (V-128) - 0.391 * (U-128)
// B = 1.164 * (Y-16) + 2.018 * (U-128)
// where Y is in the [16,235] range, and U/V in the [16,240] range.
// But the common term 1.164 * (Y-16) can be handled as an offset in the
// VP8kClip[] table. So the formulae should be read as:
// R = 1.164 * [Y + 1.371 * (V-128) ] - 18.624
// G = 1.164 * [Y - 0.698 * (V-128) - 0.336 * (U-128)] - 18.624
// B = 1.164 * [Y + 1.733 * (U-128)] - 18.624
// once factorized. Here too, 16bit fixed precision is used.
//
// Author: Skal (pascal.massimino@gmail.com)
#ifndef WEBP_DSP_YUV_H_