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

[movit] / ycbcr.cpp

diff --git a/ycbcr.cpp b/ycbcr.cpp
index f0124eaab178048a2ae3a00c758355fa275668a2..dc223e7441c845cf7c1449e439862c5732efc71f 100644 (file)
--- a/ycbcr.cpp
+++ b/ycbcr.cpp
@@ -1,3 +1,6 @@
+// Note: This file does not have its own unit test; it is tested mainly
+// through YCbCrInput's unit tests.
+

 #include <Eigen/Core>
 #include <Eigen/LU>
 
 #include <Eigen/Core>
 #include <Eigen/LU>
 


@@ -45,7 +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;
 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';
 }
 
 // Given <ycbcr_format>, compute the values needed to turn Y'CbCr into R'G'B';


@@ -82,6 +90,7 @@ void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycb
        }
 
        if (ycbcr_format.full_range) {
        }
 
        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;
                offset[0] = 0.0 / 255.0;
                offset[1] = 128.0 / 255.0;
                offset[2] = 128.0 / 255.0;


@@ -91,6 +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.
                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;
                offset[0] = 16.0 / 255.0;
                offset[1] = 128.0 / 255.0;
                offset[2] = 128.0 / 255.0;