diff options
Diffstat (limited to 'src/dsp/yuv.h')
| -rw-r--r-- | src/dsp/yuv.h | 109 |
1 files changed, 76 insertions, 33 deletions
diff --git a/src/dsp/yuv.h b/src/dsp/yuv.h index ee3587e3..add167ea 100644 --- a/src/dsp/yuv.h +++ b/src/dsp/yuv.h @@ -7,6 +7,25 @@ // // 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. +// But the common term 1.164 * (Y-16) can be handled as an offset in the +// VP8kClip[] table. So 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_ @@ -14,13 +33,15 @@ #include "../dec/decode_vp8.h" -/* - * Define ANDROID_WEBP_RGB to enable specific optimizations for Android - * RGBA_4444 & RGB_565 color support. - * - */ - -#define ANDROID_WEBP_RGB +#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 @@ -53,16 +74,16 @@ static WEBP_INLINE void VP8YuvToRgb565(uint8_t y, uint8_t u, uint8_t v, const int r_off = VP8kVToR[v]; const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX; const int b_off = VP8kUToB[u]; -#ifdef ANDROID_WEBP_RGB - rgb[1] = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) | - (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5)); - rgb[0] = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) | - (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3)); + const uint8_t rg = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) | + (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5)); + const uint8_t gb = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) | + (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3)); +#ifdef WEBP_SWAP_16BIT_CSP + rgb[0] = gb; + rgb[1] = rg; #else - rgb[0] = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) | - (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5)); - rgb[1] = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) | - (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3)); + rgb[0] = rg; + rgb[1] = gb; #endif } @@ -77,14 +98,15 @@ static WEBP_INLINE void VP8YuvToRgba4444(uint8_t y, uint8_t u, uint8_t v, const int r_off = VP8kVToR[v]; const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX; const int b_off = VP8kUToB[u]; -#ifdef ANDROID_WEBP_RGB - argb[1] = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) | - VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]); - argb[0] = 0x0f | (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4); + const uint8_t rg = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) | + VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]); + const uint8_t ba = (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4) | 0x0f; +#ifdef WEBP_SWAP_16BIT_CSP + argb[0] = ba; + argb[1] = rg; #else - argb[0] = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) | - VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]); - argb[1] = 0x0f | (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4); + argb[0] = rg; + argb[1] = ba; #endif } @@ -115,18 +137,14 @@ void VP8YUVInit(void); //------------------------------------------------------------------------------ // RGB -> YUV conversion -// 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. static WEBP_INLINE int VP8ClipUV(int v) { - v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2); - return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255; + v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2); + return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255; } +#ifndef USE_YUVj + static WEBP_INLINE int VP8RGBToY(int r, int g, int b) { const int kRound = (1 << (YUV_FIX - 1)) + (16 << YUV_FIX); const int luma = 16839 * r + 33059 * g + 6420 * b; @@ -134,13 +152,38 @@ static WEBP_INLINE int VP8RGBToY(int r, int g, int b) { } static WEBP_INLINE int VP8RGBToU(int r, int g, int b) { - return VP8ClipUV(-9719 * r - 19081 * g + 28800 * b); + const int u = -9719 * r - 19081 * g + 28800 * b; + return VP8ClipUV(u); +} + +static WEBP_INLINE int VP8RGBToV(int r, int g, int b) { + const int v = +28800 * r - 24116 * g - 4684 * b; + return VP8ClipUV(v); +} + +#else + +// This JPEG-YUV colorspace, only for comparison! +// These are also 16-bit precision coefficients from Rec.601, but with full +// [0..255] output range. +static WEBP_INLINE int VP8RGBToY(int r, int g, int b) { + const int kRound = (1 << (YUV_FIX - 1)); + const int luma = 19595 * r + 38470 * g + 7471 * b; + return (luma + kRound) >> YUV_FIX; // no need to clip +} + +static WEBP_INLINE int VP8RGBToU(int r, int g, int b) { + const int u = -11058 * r - 21710 * g + 32768 * b; + return VP8ClipUV(u); } static WEBP_INLINE int VP8RGBToV(int r, int g, int b) { - return VP8ClipUV(+28800 * r - 24116 * g - 4684 * b); + const int v = 32768 * r - 27439 * g - 5329 * b; + return VP8ClipUV(v); } +#endif // USE_YUVj + #if defined(__cplusplus) || defined(c_plusplus) } // extern "C" #endif |