Add an effect for 4:2:2 interleaved YCbCr input (UYVY).

[movit] / ycbcr.cpp

diff --git a/ycbcr.cpp b/ycbcr.cpp
new file mode 100644 (file)
index 0000000..f0124ea
--- /dev/null
+++ b/ycbcr.cpp
@@ -0,0 +1,126 @@
+#include <Eigen/Core>
+#include <Eigen/LU>
+
+#include "ycbcr.h"
+
+using namespace Eigen;
+
+namespace movit {
+
+// OpenGL has texel center in (0.5, 0.5), but different formats have
+// chroma in various other places. If luma samples are X, the chroma
+// sample is *, and subsampling is 3x3, the situation with chroma
+// center in (0.5, 0.5) looks approximately like this:
+//
+//   X   X
+//     *   
+//   X   X
+//
+// If, on the other hand, chroma center is in (0.0, 0.5) (common
+// for e.g. MPEG-4), the figure changes to:
+//
+//   X   X
+//   *      
+//   X   X
+//
+// In other words, (0.0, 0.0) means that the chroma sample is exactly
+// co-sited on top of the top-left luma sample. Note, however, that
+// this is _not_ 0.5 texels to the left, since the OpenGL's texel center
+// is in (0.5, 0.5); it is in (0.25, 0.25). In a sense, the four luma samples
+// define a square where chroma position (0.0, 0.0) is in texel position
+// (0.25, 0.25) and chroma position (1.0, 1.0) is in texel position (0.75, 0.75)
+// (the outer border shows the borders of the texel itself, ie. from
+// (0, 0) to (1, 1)):
+//
+//  ---------
+// |         |
+// |  X---X  |
+// |  | * |  |
+// |  X---X  |
+// |         |
+//  ---------
+//
+// Also note that if we have no subsampling, the square will have zero
+// area and the chroma position does not matter at all.
+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;
+}
+
+// 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)
+{
+       double coeff[3], 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.
+       *ycbcr_to_rgb = rgb_to_ycbcr.inverse();
+
+       // Fold in the scaling.
+       *ycbcr_to_rgb *= Map<const Vector3d>(scale).asDiagonal();
+}
+
+}  // namespace movit