Prepare for better understanding of 10- and 12-bit Y'CbCr.

[movit] / ycbcr.cpp

diff --git a/ycbcr.cpp b/ycbcr.cpp
index 08c8cd25d4603c43b092abe078b6d98815a466e9..dc223e7441c845cf7c1449e439862c5732efc71f 100644 (file)
--- a/ycbcr.cpp
+++ b/ycbcr.cpp
@@ -48,7 +48,12 @@ namespace movit {
 float compute_chroma_offset(float pos, unsigned subsampling_factor, unsigned resolution)
 {
        float local_chroma_pos = (0.5 + pos * (subsampling_factor - 1)) / subsampling_factor;
-       return (0.5 - local_chroma_pos) / resolution;
+       if (fabs(local_chroma_pos - 0.5) < 1e-10) {
+               // x + (-0) can be optimized away freely, as opposed to x + 0.
+               return -0.0;
+       } else {
+               return (0.5 - local_chroma_pos) / resolution;
+       }
 }
 
 // Given <ycbcr_format>, compute the values needed to turn Y'CbCr into R'G'B';
@@ -85,6 +90,7 @@ void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycb
        }
 
        if (ycbcr_format.full_range) {
+               // TODO: Use num_levels.
                offset[0] = 0.0 / 255.0;
                offset[1] = 128.0 / 255.0;
                offset[2] = 128.0 / 255.0;
@@ -94,6 +100,7 @@ void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycb
                scale[2] = 1.0;
        } else {
                // Rec. 601, page 4; Rec. 709, page 19; Rec. 2020, page 4.
+               // TODO: Use num_levels.
                offset[0] = 16.0 / 255.0;
                offset[1] = 128.0 / 255.0;
                offset[2] = 128.0 / 255.0;