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++ // Copyright 2022 Google Inc. All Rights Reserved.
++ //
++ // Use of this source code is governed by a BSD-style license
++ // that can be found in the COPYING file in the root of the source
++ // tree. An additional intellectual property rights grant can be found
++ // in the file PATENTS. All contributing project authors may
++ // be found in the AUTHORS file in the root of the source tree.
++ // -----------------------------------------------------------------------------
++ //
++ // Colorspace utilities.
++
++ #include "sharpyuv/sharpyuv_csp.h"
++
++ #include <assert.h>
++ #include <math.h>
++ #include <stddef.h>
++
++ #include "sharpyuv/sharpyuv.h"
++
++ static int ToFixed16(float f) { return (int)floor(f * (1 << 16) + 0.5f); }
++
++ void SharpYuvComputeConversionMatrix(const SharpYuvColorSpace* yuv_color_space,
++ SharpYuvConversionMatrix* matrix) {
++ const float kr = yuv_color_space->kr;
++ const float kb = yuv_color_space->kb;
++ const float kg = 1.0f - kr - kb;
++ const float cb = 0.5f / (1.0f - kb);
++ const float cr = 0.5f / (1.0f - kr);
++
++ const int shift = yuv_color_space->bit_depth - 8;
++
++ const float denom = (float)((1 << yuv_color_space->bit_depth) - 1);
++ float scale_y = 1.0f;
++ float add_y = 0.0f;
++ float scale_u = cb;
++ float scale_v = cr;
++ float add_uv = (float)(128 << shift);
++ assert(yuv_color_space->bit_depth >= 8);
++
++ if (yuv_color_space->range == kSharpYuvRangeLimited) {
++ scale_y *= (219 << shift) / denom;
++ scale_u *= (224 << shift) / denom;
++ scale_v *= (224 << shift) / denom;
++ add_y = (float)(16 << shift);
++ }
++
++ matrix->rgb_to_y[0] = ToFixed16(kr * scale_y);
++ matrix->rgb_to_y[1] = ToFixed16(kg * scale_y);
++ matrix->rgb_to_y[2] = ToFixed16(kb * scale_y);
++ matrix->rgb_to_y[3] = ToFixed16(add_y);
++
++ matrix->rgb_to_u[0] = ToFixed16(-kr * scale_u);
++ matrix->rgb_to_u[1] = ToFixed16(-kg * scale_u);
++ matrix->rgb_to_u[2] = ToFixed16((1 - kb) * scale_u);
++ matrix->rgb_to_u[3] = ToFixed16(add_uv);
++
++ matrix->rgb_to_v[0] = ToFixed16((1 - kr) * scale_v);
++ matrix->rgb_to_v[1] = ToFixed16(-kg * scale_v);
++ matrix->rgb_to_v[2] = ToFixed16(-kb * scale_v);
++ matrix->rgb_to_v[3] = ToFixed16(add_uv);
++ }
++
++ // Matrices are in YUV_FIX fixed point precision.
++ // WebP's matrix, similar but not identical to kRec601LimitedMatrix
++ // Derived using the following formulas:
++ // Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16
++ // U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128
++ // V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128
++ static const SharpYuvConversionMatrix kWebpMatrix = {
++ {16839, 33059, 6420, 16 << 16},
++ {-9719, -19081, 28800, 128 << 16},
++ {28800, -24116, -4684, 128 << 16},
++ };
++ // Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeLimited
++ static const SharpYuvConversionMatrix kRec601LimitedMatrix = {
++ {16829, 33039, 6416, 16 << 16},
++ {-9714, -19071, 28784, 128 << 16},
++ {28784, -24103, -4681, 128 << 16},
++ };
++ // Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeFull
++ static const SharpYuvConversionMatrix kRec601FullMatrix = {
++ {19595, 38470, 7471, 0},
++ {-11058, -21710, 32768, 128 << 16},
++ {32768, -27439, -5329, 128 << 16},
++ };
++ // Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeLimited
++ static const SharpYuvConversionMatrix kRec709LimitedMatrix = {
++ {11966, 40254, 4064, 16 << 16},
++ {-6596, -22189, 28784, 128 << 16},
++ {28784, -26145, -2639, 128 << 16},
++ };
++ // Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeFull
++ static const SharpYuvConversionMatrix kRec709FullMatrix = {
++ {13933, 46871, 4732, 0},
++ {-7509, -25259, 32768, 128 << 16},
++ {32768, -29763, -3005, 128 << 16},
++ };
++
++ const SharpYuvConversionMatrix* SharpYuvGetConversionMatrix(
++ SharpYuvMatrixType matrix_type) {
++ switch (matrix_type) {
++ case kSharpYuvMatrixWebp:
++ return &kWebpMatrix;
++ case kSharpYuvMatrixRec601Limited:
++ return &kRec601LimitedMatrix;
++ case kSharpYuvMatrixRec601Full:
++ return &kRec601FullMatrix;
++ case kSharpYuvMatrixRec709Limited:
++ return &kRec709LimitedMatrix;
++ case kSharpYuvMatrixRec709Full:
++ return &kRec709FullMatrix;
++ case kSharpYuvMatrixNum:
++ return NULL;
++ }
++ return NULL;
++ }