// Given <ycbcr_format>, compute the values needed to turn Y'CbCr into R'G'B';
// first subtract the returned offset, then left-multiply the returned matrix
// (the scaling is already folded into it).
-void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycbcr_to_rgb)
+void compute_ycbcr_matrix(YCbCrFormat ycbcr_format, float* offset, Matrix3d* ycbcr_to_rgb, GLenum type, double *scale_factor)
{
double coeff[3], scale[3];
assert(false);
}
+ int num_levels = ycbcr_format.num_levels;
+ if (num_levels == 0) {
+ // For the benefit of clients using old APIs, but still zeroing out the structure.
+ num_levels = 256;
+ }
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 / (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.
- // TODO: Use num_levels.
- 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.
// Fold in the scaling.
*ycbcr_to_rgb *= Map<const Vector3d>(scale).asDiagonal();
+
+ if (type == GL_UNSIGNED_SHORT) {
+ // For 10-bit or 12-bit packed into 16-bit, we need to scale the values
+ // so that the max value goes from 1023 (or 4095) to 65535. We do this
+ // by folding the scaling into the conversion matrix, so it comes essentially
+ // for free. However, the offset is before the scaling (and thus assumes
+ // correctly scaled values), so we need to adjust that the other way.
+ double scale = 65535.0 / (ycbcr_format.num_levels - 1);
+ offset[0] /= scale;
+ offset[1] /= scale;
+ offset[2] /= scale;
+ *ycbcr_to_rgb *= scale;
+ if (scale_factor != nullptr) {
+ *scale_factor = scale;
+ }
+ } else if (scale_factor != nullptr) {
+ *scale_factor = 1.0;
+ }
}
} // namespace movit