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// Copyright 2010 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.
// -----------------------------------------------------------------------------
//
// inline YUV<->RGB conversion function
//
// The exact naming is Y'CbCr, following the ITU-R BT.601 standard.
// More information at: http://en.wikipedia.org/wiki/YCbCr
// 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
// We use 16bit fixed point operations for RGB->YUV conversion (YUV_FIX).
//
// For the Y'CbCr to RGB conversion, the BT.601 specification reads:
//   R = 1.164 * (Y-16) + 1.596 * (V-128)
//   G = 1.164 * (Y-16) - 0.813 * (V-128) - 0.391 * (U-128)
//   B = 1.164 * (Y-16)                   + 2.018 * (U-128)
// where Y is in the [16,235] range, and U/V in the [16,240] range.
// In the table-lookup version (WEBP_YUV_USE_TABLE), the common factor
// "1.164 * (Y-16)" can be handled as an offset in the VP8kClip[] table.
// So in this case the formulae should read:
//   R = 1.164 * [Y + 1.371 * (V-128)                  ] - 18.624
//   G = 1.164 * [Y - 0.698 * (V-128) - 0.336 * (U-128)] - 18.624
//   B = 1.164 * [Y                   + 1.733 * (U-128)] - 18.624
// once factorized.
// For YUV->RGB conversion, only 14bit fixed precision is used (YUV_FIX2).
// That's the maximum possible for a convenient ARM implementation.
//
// Author: Skal (pascal.massimino@gmail.com)

#ifndef WEBP_DSP_YUV_H_
#define WEBP_DSP_YUV_H_

#include "./dsp.h"
#include "../dec/decode_vp8.h"

// Define the following to use the LUT-based code:
// #define WEBP_YUV_USE_TABLE

#if defined(WEBP_EXPERIMENTAL_FEATURES)
// Do NOT activate this feature for real compression. This is only experimental!
// This flag is for comparison purpose against JPEG's "YUVj" natural colorspace.
// This colorspace is close to Rec.601's Y'CbCr model with the notable
// difference of allowing larger range for luma/chroma.
// See http://en.wikipedia.org/wiki/YCbCr#JPEG_conversion paragraph, and its
// difference with http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
// #define USE_YUVj
#endif

//------------------------------------------------------------------------------
// YUV -> RGB conversion

#ifdef __cplusplus
extern "C" {
#endif

enum {
  YUV_FIX = 16,                    // fixed-point precision for RGB->YUV
  YUV_HALF = 1 << (YUV_FIX - 1),
  YUV_MASK = (256 << YUV_FIX) - 1,
  YUV_RANGE_MIN = -227,            // min value of r/g/b output
  YUV_RANGE_MAX = 256 + 226,       // max value of r/g/b output

  YUV_FIX2 = 14,                   // fixed-point precision for YUV->RGB
  YUV_HALF2 = 1 << (YUV_FIX2 - 1),
  YUV_MASK2 = (256 << YUV_FIX2) - 1
};

// These constants are 14b fixed-point version of ITU-R BT.601 constants.
#define kYScale 19077    // 1.164 = 255 / 219
#define kVToR   26149    // 1.596 = 255 / 112 * 0.701
#define kUToG   6419     // 0.391 = 255 / 112 * 0.886 * 0.114 / 0.587
#define kVToG   13320    // 0.813 = 255 / 112 * 0.701 * 0.299 / 0.587
#define kUToB   33050    // 2.018 = 255 / 112 * 0.886
#define kRCst (-kYScale * 16 - kVToR * 128 + YUV_HALF2)
#define kGCst (-kYScale * 16 + kUToG * 128 + kVToG * 128 + YUV_HALF2)
#define kBCst (-kYScale * 16 - kUToB * 128 + YUV_HALF2)

//------------------------------------------------------------------------------

#if !defined(WEBP_YUV_USE_TABLE)