view release on metacpan or  search on metacpan

webp-src/src/dsp/yuv.h  view on Meta::CPAN

// Copyright 2010 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
//  Software License Agreement:  http://www.webmproject.org/license/software/
//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// 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.
//
// 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 be read as:
//   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. Here too, 16bit fixed precision is used.
//
// Author: Skal (pascal.massimino@gmail.com)

#ifndef WEBP_DSP_YUV_H_
#define WEBP_DSP_YUV_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

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

enum { YUV_FIX = 16,                // fixed-point precision
       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
};

#ifdef WEBP_YUV_USE_TABLE

extern int16_t VP8kVToR[256], VP8kUToB[256];
extern int32_t VP8kVToG[256], VP8kUToG[256];
extern uint8_t VP8kClip[YUV_RANGE_MAX - YUV_RANGE_MIN];
extern uint8_t VP8kClip4Bits[YUV_RANGE_MAX - YUV_RANGE_MIN];

static WEBP_INLINE void VP8YuvToRgb(uint8_t y, uint8_t u, uint8_t v,
                                    uint8_t* const rgb) {
  const int r_off = VP8kVToR[v];
  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
  const int b_off = VP8kUToB[u];
  rgb[0] = VP8kClip[y + r_off - YUV_RANGE_MIN];
  rgb[1] = VP8kClip[y + g_off - YUV_RANGE_MIN];
  rgb[2] = VP8kClip[y + b_off - YUV_RANGE_MIN];
}

static WEBP_INLINE void VP8YuvToBgr(uint8_t y, uint8_t u, uint8_t v,
                                    uint8_t* const bgr) {
  const int r_off = VP8kVToR[v];
  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;