libsharpyuv: add colorspace utilities

Change-Id: I620c8593dc81f39e747de5ed354332adb7278bed

sharpyuv/sharpyuv_csp.c

@@ -0,0 +1,111 @@
+// 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 <string.h>
+
+static int ToFixed16(float f) { return (int)round(f * (1 << 16)); }
+
+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 cr = 0.5f / (1.0f - kb);
+  const float cb = 0.5f / (1.0f - kr);
+
+  const int shift = yuv_color_space->bits - 8;
+
+  const float denom = (float)((1 << yuv_color_space->bits) - 1);
+  float scaleY = 1.0f;
+  float addY = 0.0f;
+  float scaleU = cr;
+  float scaleV = cb;
+  float addUV = (128 << shift);
+
+  assert(yuv_color_space->bits >= 8);
+
+  if (yuv_color_space->range == kSharpYuvRangeLimited) {
+    scaleY *= (219 << shift) / denom;
+    scaleU *= (224 << shift) / denom;
+    scaleV *= (224 << shift) / denom;
+    addY = (16 << shift);
+  }
+
+  matrix->rgb_to_y[0] = ToFixed16(kr * scaleY);
+  matrix->rgb_to_y[1] = ToFixed16(kg * scaleY);
+  matrix->rgb_to_y[2] = ToFixed16(kb * scaleY);
+  matrix->rgb_to_y[3] = ToFixed16(addY);
+
+  matrix->rgb_to_u[0] = ToFixed16(-kr * scaleU);
+  matrix->rgb_to_u[1] = ToFixed16(-kg * scaleU);
+  matrix->rgb_to_u[2] = ToFixed16((1 - kb) * scaleU);
+  matrix->rgb_to_u[3] = ToFixed16(addUV);
+
+  matrix->rgb_to_v[0] = ToFixed16((1 - kr) * scaleV);
+  matrix->rgb_to_v[1] = ToFixed16(-kg * scaleV);
+  matrix->rgb_to_v[2] = ToFixed16(-kb * scaleV);
+  matrix->rgb_to_v[3] = ToFixed16(addUV);
+}
+
+// Matrices are in YUV_FIX fixed point precision.
+// WebP's matrix, similar but not identical to kRec601LimitedMatrix.
+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 btits=8 range=kLimited
+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 btits=8 range=kFull
+static const SharpYuvConversionMatrix kRec601FullMatrix = {
+  {19595, 38470, 7471, 0},
+  {-11058, -21710, 32768, 128 << 16},
+  {32768, -27439, -5329, 128 << 16},
+};
+// Kr=0.2126f Kb=0.0722f bits=8 range=kLimited
+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 bits=8 range=kFull
+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 kSharpYuvMarixRec601Limited:
+      return &kRec601LimitedMatrix;
+    case kSharpYuvMarixRec601Full:
+      return &kRec601FullMatrix;
+    case kSharpYuvMarixRec709Limited:
+      return &kRec709LimitedMatrix;
+    case kSharpYuvMarixRec709Full:
+      return &kRec709FullMatrix;
+    case kSharpYuvMarixNum:
+      return NULL;
+  }
+  return NULL;
+}