From e40176be4c5849320531f98606a933f3e95ac030 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Wed, 29 Jul 2015 13:53:59 +0200 Subject: [PATCH] Small refactoring in YCbCrInput. --- ycbcr_input.cpp | 147 +++++++++++++++++++++++++----------------------- 1 file changed, 78 insertions(+), 69 deletions(-) diff --git a/ycbcr_input.cpp b/ycbcr_input.cpp index 6cf3116..ee341f0 100644 --- a/ycbcr_input.cpp +++ b/ycbcr_input.cpp @@ -58,6 +58,81 @@ float compute_chroma_offset(float pos, unsigned subsampling_factor, unsigned res return (0.5 - local_chroma_pos) / resolution; } +// Given , 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(scale).asDiagonal(); +} + } // namespace YCbCrInput::YCbCrInput(const ImageFormat &image_format, @@ -140,75 +215,9 @@ void YCbCrInput::set_gl_state(GLuint glsl_program_num, const string& prefix, uns string YCbCrInput::output_fragment_shader() { - 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(scale).asDiagonal(); + float offset[3]; + Matrix3d ycbcr_to_rgb; + compute_ycbcr_matrix(ycbcr_format, offset, &ycbcr_to_rgb); string frag_shader; -- 2.39.2