diff --git a/sharpyuv/sharpyuv_csp.c b/sharpyuv/sharpyuv_csp.c index b425a906..ae03523e 100644 --- a/sharpyuv/sharpyuv_csp.c +++ b/sharpyuv/sharpyuv_csp.c @@ -60,6 +60,10 @@ void SharpYuvComputeConversionMatrix(const SharpYuvColorSpace* yuv_color_space, // Matrices are in YUV_FIX fixed point precision. // WebP's matrix, similar but not identical to kRec601LimitedMatrix +// Derived using the following formulas: +// Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16 +// U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128 +// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128 static const SharpYuvConversionMatrix kWebpMatrix = { {16839, 33059, 6420, 16 << 16}, {-9719, -19081, 28800, 128 << 16}, diff --git a/src/dsp/yuv.h b/src/dsp/yuv.h index 91fdba12..59b871ae 100644 --- a/src/dsp/yuv.h +++ b/src/dsp/yuv.h @@ -11,15 +11,15 @@ // // The exact naming is Y'CbCr, following the ITU-R BT.601 standard. // More information at: https://en.wikipedia.org/wiki/YCbCr -// Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16 -// U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128 -// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128 +// Y = 0.2568 * R + 0.5041 * G + 0.0979 * B + 16 +// U = -0.1482 * R - 0.2910 * G + 0.4392 * B + 128 +// V = 0.4392 * R - 0.3678 * G - 0.0714 * B + 128 // We use 16bit fixed point operations for RGB->YUV conversion (YUV_FIX). // // 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) +// G = 1.164 * (Y-16) - 0.813 * (V-128) - 0.392 * (U-128) +// B = 1.164 * (Y-16) + 2.017 * (U-128) // where Y is in the [16,235] range, and U/V in the [16,240] range. // // The fixed-point implementation used here is: