X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=ycbcr.cpp;h=eaa2ee8c3bb277903bef8ab7a8a33f6c137aecf1;hp=f0124eaab178048a2ae3a00c758355fa275668a2;hb=25162b5457057af3ebcc1649571eeeb923e90098;hpb=ba60914d4e5eda7b28af700bf43e9699b7aa720d

diff --git a/ycbcr.cpp b/ycbcr.cpp
index f0124ea..eaa2ee8 100644
--- a/ycbcr.cpp
+++ b/ycbcr.cpp
@@ -1,3 +1,6 @@
+// Note: These functions are tested in ycbcr_input_test.cpp; both through some
+// direct matrix tests, but most of all through YCbCrInput's unit tests.
+
 #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;
-	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';
@@ -81,23 +89,26 @@ void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycb
 		assert(false);
 	}
 
+	const int num_levels = ycbcr_format.num_levels;
 	if (ycbcr_format.full_range) {
-		offset[0] = 0.0 / 255.0;
-		offset[1] = 128.0 / 255.0;
-		offset[2] = 128.0 / 255.0;
+		offset[0] = 0.0 / (num_levels - 1);
+		offset[1] = double(num_levels / 2) / (num_levels - 1);  // E.g. 128/255.
+		offset[2] = double(num_levels / 2) / (num_levels - 1);
 
 		scale[0] = 1.0;
 		scale[1] = 1.0;
 		scale[2] = 1.0;
 	} else {
-		// Rec. 601, page 4; Rec. 709, page 19; Rec. 2020, page 4.
-		offset[0] = 16.0 / 255.0;
-		offset[1] = 128.0 / 255.0;
-		offset[2] = 128.0 / 255.0;
-
-		scale[0] = 255.0 / 219.0;
-		scale[1] = 255.0 / 224.0;
-		scale[2] = 255.0 / 224.0;
+		// Rec. 601, page 4; Rec. 709, page 19; Rec. 2020, page 5.
+		// Rec. 2020 contains the most generic formulas, which we use here.
+		const double s = num_levels / 256.0;  // 2^(n-8) in Rec. 2020 parlance.
+		offset[0] = (s * 16.0) / (num_levels - 1);
+		offset[1] = (s * 128.0) / (num_levels - 1);
+		offset[2] = (s * 128.0) / (num_levels - 1);
+
+		scale[0] = double(num_levels - 1) / (s * 219.0);
+		scale[1] = double(num_levels - 1) / (s * 224.0);
+		scale[2] = double(num_levels - 1) / (s * 224.0);
 	}
 
 	// Matrix to convert RGB to YCbCr. See e.g. Rec. 601.
@@ -106,12 +117,12 @@ void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycb
 	rgb_to_ycbcr(0,1) = coeff[1];
 	rgb_to_ycbcr(0,2) = coeff[2];
 
-	float cb_fac = (224.0 / 219.0) / (coeff[0] + coeff[1] + 1.0f - coeff[2]);
+	float cb_fac = 1.0 / (coeff[0] + coeff[1] + 1.0f - coeff[2]);
 	rgb_to_ycbcr(1,0) = -coeff[0] * cb_fac;
 	rgb_to_ycbcr(1,1) = -coeff[1] * cb_fac;
 	rgb_to_ycbcr(1,2) = (1.0f - coeff[2]) * cb_fac;
 
-	float cr_fac = (224.0 / 219.0) / (1.0f - coeff[0] + coeff[1] + coeff[2]);
+	float cr_fac = 1.0 / (1.0f - coeff[0] + coeff[1] + coeff[2]);
 	rgb_to_ycbcr(2,0) = (1.0f - coeff[0]) * cr_fac;
 	rgb_to_ycbcr(2,1) = -coeff[1] * cr_fac;
 	rgb_to_ycbcr(2,2) = -coeff[2] * cr_fac;