yuv.h revision 4b2196c929b70f2cdc1c2556580d349db89356d8 
1// Copyright 2010 Google Inc. All Rights Reserved.
2//
3// This code is licensed under the same terms as WebM:
4//  Software License Agreement:  http://www.webmproject.org/license/software/
5//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
6// -----------------------------------------------------------------------------
7//
8// inline YUV<->RGB conversion function
9//
10// The exact naming is Y'CbCr, following the ITU-R BT.601 standard.
11// More information at: http://en.wikipedia.org/wiki/YCbCr
12// Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16
13// U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128
14// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128
15// We use 16bit fixed point operations for RGB->YUV conversion.
16//
17// For the Y'CbCr to RGB conversion, the BT.601 specification reads:
18//   R = 1.164 * (Y-16) + 1.596 * (V-128)
19//   G = 1.164 * (Y-16) - 0.813 * (V-128) - 0.391 * (U-128)
20//   B = 1.164 * (Y-16)                   + 2.018 * (U-128)
21// where Y is in the [16,235] range, and U/V in the [16,240] range.
22// But the common term 1.164 * (Y-16) can be handled as an offset in the
23// VP8kClip[] table. So the formulae should be read as:
24//   R = 1.164 * [Y + 1.371 * (V-128)                  ] - 18.624
25//   G = 1.164 * [Y - 0.698 * (V-128) - 0.336 * (U-128)] - 18.624
26//   B = 1.164 * [Y                   + 1.733 * (U-128)] - 18.624
27// once factorized. Here too, 16bit fixed precision is used.
28//
29// Author: Skal (pascal.massimino@gmail.com)
30
31#ifndef WEBP_DSP_YUV_H_
32#define WEBP_DSP_YUV_H_
33
34#include "../dec/decode_vp8.h"
35
36#if defined(WEBP_EXPERIMENTAL_FEATURES)
37// Do NOT activate this feature for real compression. This is only experimental!
38// This flag is for comparison purpose against JPEG's "YUVj" natural colorspace.
39// This colorspace is close to Rec.601's Y'CbCr model with the notable
40// difference of allowing larger range for luma/chroma.
41// See http://en.wikipedia.org/wiki/YCbCr#JPEG_conversion paragraph, and its
42// difference with http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
43// #define USE_YUVj
44#endif
45
46//------------------------------------------------------------------------------
47// YUV -> RGB conversion
48
49#if defined(__cplusplus) || defined(c_plusplus)
50extern "C" {
51#endif
52
53enum { YUV_FIX = 16,                // fixed-point precision
54       YUV_RANGE_MIN = -227,        // min value of r/g/b output
55       YUV_RANGE_MAX = 256 + 226    // max value of r/g/b output
56};
57extern int16_t VP8kVToR[256], VP8kUToB[256];
58extern int32_t VP8kVToG[256], VP8kUToG[256];
59extern uint8_t VP8kClip[YUV_RANGE_MAX - YUV_RANGE_MIN];
60extern uint8_t VP8kClip4Bits[YUV_RANGE_MAX - YUV_RANGE_MIN];
61
62static WEBP_INLINE void VP8YuvToRgb(uint8_t y, uint8_t u, uint8_t v,
63                                    uint8_t* const rgb) {
64  const int r_off = VP8kVToR[v];
65  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
66  const int b_off = VP8kUToB[u];
67  rgb[0] = VP8kClip[y + r_off - YUV_RANGE_MIN];
68  rgb[1] = VP8kClip[y + g_off - YUV_RANGE_MIN];
69  rgb[2] = VP8kClip[y + b_off - YUV_RANGE_MIN];
70}
71
72static WEBP_INLINE void VP8YuvToRgb565(uint8_t y, uint8_t u, uint8_t v,
73                                       uint8_t* const rgb) {
74  const int r_off = VP8kVToR[v];
75  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
76  const int b_off = VP8kUToB[u];
77  const uint8_t rg = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) |
78                      (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5));
79  const uint8_t gb = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) |
80                      (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3));
81#ifdef WEBP_SWAP_16BIT_CSP
82  rgb[0] = gb;
83  rgb[1] = rg;
84#else
85  rgb[0] = rg;
86  rgb[1] = gb;
87#endif
88}
89
90static WEBP_INLINE void VP8YuvToArgb(uint8_t y, uint8_t u, uint8_t v,
91                                     uint8_t* const argb) {
92  argb[0] = 0xff;
93  VP8YuvToRgb(y, u, v, argb + 1);
94}
95
96static WEBP_INLINE void VP8YuvToRgba4444(uint8_t y, uint8_t u, uint8_t v,
97                                         uint8_t* const argb) {
98  const int r_off = VP8kVToR[v];
99  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
100  const int b_off = VP8kUToB[u];
101  const uint8_t rg = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) |
102                      VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]);
103  const uint8_t ba = (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4) | 0x0f;
104#ifdef WEBP_SWAP_16BIT_CSP
105  argb[0] = ba;
106  argb[1] = rg;
107#else
108  argb[0] = rg;
109  argb[1] = ba;
110#endif
111}
112
113static WEBP_INLINE void VP8YuvToBgr(uint8_t y, uint8_t u, uint8_t v,
114                                    uint8_t* const bgr) {
115  const int r_off = VP8kVToR[v];
116  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
117  const int b_off = VP8kUToB[u];
118  bgr[0] = VP8kClip[y + b_off - YUV_RANGE_MIN];
119  bgr[1] = VP8kClip[y + g_off - YUV_RANGE_MIN];
120  bgr[2] = VP8kClip[y + r_off - YUV_RANGE_MIN];
121}
122
123static WEBP_INLINE void VP8YuvToBgra(uint8_t y, uint8_t u, uint8_t v,
124                                     uint8_t* const bgra) {
125  VP8YuvToBgr(y, u, v, bgra);
126  bgra[3] = 0xff;
127}
128
129static WEBP_INLINE void VP8YuvToRgba(uint8_t y, uint8_t u, uint8_t v,
130                                     uint8_t* const rgba) {
131  VP8YuvToRgb(y, u, v, rgba);
132  rgba[3] = 0xff;
133}
134
135// Must be called before everything, to initialize the tables.
136void VP8YUVInit(void);
137
138//------------------------------------------------------------------------------
139// RGB -> YUV conversion
140
141static WEBP_INLINE int VP8ClipUV(int v) {
142  v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2);
143  return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255;
144}
145
146#ifndef USE_YUVj
147
148static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
149  const int kRound = (1 << (YUV_FIX - 1)) + (16 << YUV_FIX);
150  const int luma = 16839 * r + 33059 * g + 6420 * b;
151  return (luma + kRound) >> YUV_FIX;  // no need to clip
152}
153
154static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
155  const int u = -9719 * r - 19081 * g + 28800 * b;
156  return VP8ClipUV(u);
157}
158
159static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
160  const int v = +28800 * r - 24116 * g - 4684 * b;
161  return VP8ClipUV(v);
162}
163
164#else
165
166// This JPEG-YUV colorspace, only for comparison!
167// These are also 16-bit precision coefficients from Rec.601, but with full
168// [0..255] output range.
169static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
170  const int kRound = (1 << (YUV_FIX - 1));
171  const int luma = 19595 * r + 38470 * g + 7471 * b;
172  return (luma + kRound) >> YUV_FIX;  // no need to clip
173}
174
175static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
176  const int u = -11058 * r - 21710 * g + 32768 * b;
177  return VP8ClipUV(u);
178}
179
180static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
181  const int v = 32768 * r - 27439 * g - 5329 * b;
182  return VP8ClipUV(v);
183}
184
185#endif    // USE_YUVj
186
187#if defined(__cplusplus) || defined(c_plusplus)
188}    // extern "C"
189#endif
190
191#endif  /* WEBP_DSP_YUV_H_ */
192