- float coeff[3], offset[3];
- double scale[3];
-
- switch (ycbcr_format.luma_coefficients) {
- case YCBCR_REC_601:
- // Rec. 601, page 2.
- coeff[0] = 0.299;
- coeff[1] = 0.587;
- coeff[2] = 0.114;
- break;
-
- case YCBCR_REC_709:
- // Rec. 709, page 19.
- coeff[0] = 0.2126;
- coeff[1] = 0.7152;
- coeff[2] = 0.0722;
- break;
-
- case YCBCR_REC_2020:
- // Rec. 2020, page 4.
- coeff[0] = 0.2627;
- coeff[1] = 0.6780;
- coeff[2] = 0.0593;
- break;
-
- default:
- assert(false);
- }
-
- if (ycbcr_format.full_range) {
- offset[0] = 0.0 / 255.0;
- offset[1] = 128.0 / 255.0;
- offset[2] = 128.0 / 255.0;
-
- 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;
- }
-
- // Matrix to convert RGB to YCbCr. See e.g. Rec. 601.
- Matrix3d rgb_to_ycbcr;
- rgb_to_ycbcr(0,0) = coeff[0];
- 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]);
- 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]);
- 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;
-
- // Inverting the matrix gives us what we need to go from YCbCr back to RGB.
- Matrix3d ycbcr_to_rgb = rgb_to_ycbcr.inverse();
-
- // Fold in the scaling.
- ycbcr_to_rgb *= Map<const Vector3d>(scale).asDiagonal();