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simplify smart RGB->YUV conversion code

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* use the same TFIX == YFIX precision (2bits)
* use int instead of float in LinearToGammaF()

output is visually equivalent. Code is a little faster.

Change-Id: Ie3cfebca351dbcbd924b3d00801d6523dca6981f
This commit is contained in:
Pascal Massimino 2015-01-23 14:42:32 +01:00
parent 0d5b334ee8
commit 0f027a72bf
1 changed files with 16 additions and 33 deletions
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49
src/enc/picture_csp.c
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@ -165,7 +165,7 @@ static const int kMinDimensionIterativeConversion = 4;
typedef int16_t fixed_t; // signed type with extra TFIX precision for UV
typedef uint16_t fixed_y_t; // unsigned type with extra YFIX precision for W
#define TFIX 6 // fixed-point precision of RGB
#define TFIX 2 // fixed-point precision of RGB
#define YFIX 2 // fixed point precision for Y/W
#define THALF ((1 << TFIX) >> 1)
@ -203,14 +203,14 @@ static WEBP_INLINE float GammaToLinearF(int v) {
return kGammaToLinearTabF[v];
}
static WEBP_INLINE float LinearToGammaF(float value) {
static WEBP_INLINE int LinearToGammaF(float value) {
const float v = value * kGammaTabSize;
const int tab_pos = (int)v;
const float x = v - (float)tab_pos; // fractional part
const float v0 = kLinearToGammaTabF[tab_pos + 0];
const float v1 = kLinearToGammaTabF[tab_pos + 1];
const float y = v1 * x + v0 * (1.f - x); // interpolate
return y;
return (int)(y + .5);
}
#else
@ -220,8 +220,8 @@ static WEBP_INLINE float GammaToLinearF(int v) {
const float norm = 1.f / MAX_Y_T;
return norm * v;
}
static WEBP_INLINE float LinearToGammaF(float value) {
return MAX_Y_T * value;
static WEBP_INLINE int LinearToGammaF(float value) {
return (int)(MAX_Y_T * value + .5);
}
#endif // USE_GAMMA_COMPRESSION
@ -229,25 +229,8 @@ static WEBP_INLINE float LinearToGammaF(float value) {
//------------------------------------------------------------------------------
// precision: YFIX -> TFIX
static WEBP_INLINE int FixedYToW(int v) {
#if TFIX == YFIX
return v;
#elif TFIX >= YFIX
return v << (TFIX - YFIX);
#else
return v >> (YFIX - TFIX);
#endif
}
static WEBP_INLINE int FixedWToY(int v) {
#if TFIX == YFIX
return v;
#elif YFIX >= TFIX
return v << (YFIX - TFIX);
#else
return v >> (TFIX - YFIX);
#endif
}
static WEBP_INLINE int FixedYToW(int v) { return v; }
static WEBP_INLINE int FixedWToY(int v) { return v; }
static uint8_t clip_8b(fixed_t v) {
return (!(v & ~0xff)) ? (uint8_t)v : (v < 0) ? 0u : 255u;
@ -275,7 +258,7 @@ static float RGBToGrayF(float r, float g, float b) {
return 0.299f * r + 0.587f * g + 0.114f * b;
}
static float ScaleDown(int a, int b, int c, int d) {
static int ScaleDown(int a, int b, int c, int d) {
const float A = GammaToLinearF(a);
const float B = GammaToLinearF(b);
const float C = GammaToLinearF(c);
@ -289,7 +272,7 @@ static WEBP_INLINE void UpdateW(const fixed_y_t* src, fixed_y_t* dst, int len) {
const float G = GammaToLinearF(src[1]);
const float B = GammaToLinearF(src[2]);
const float Y = RGBToGrayF(R, G, B);
*dst++ = (fixed_y_t)(LinearToGammaF(Y) + .5);
*dst++ = (fixed_y_t)LinearToGammaF(Y);
src += 3;
}
}
@ -298,13 +281,13 @@ static WEBP_INLINE void UpdateChroma(const fixed_y_t* src1,
const fixed_y_t* src2,
fixed_t* dst, fixed_y_t* tmp, int len) {
while (len--> 0) {
const float r = ScaleDown(src1[0], src1[3], src2[0], src2[3]);
const float g = ScaleDown(src1[1], src1[4], src2[1], src2[4]);
const float b = ScaleDown(src1[2], src1[5], src2[2], src2[5]);
const float W = RGBToGrayF(r, g, b);
dst[0] = (fixed_t)FixedYToW((int)(r - W));
dst[1] = (fixed_t)FixedYToW((int)(g - W));
dst[2] = (fixed_t)FixedYToW((int)(b - W));
const int r = ScaleDown(src1[0], src1[3], src2[0], src2[3]);
const int g = ScaleDown(src1[1], src1[4], src2[1], src2[4]);
const int b = ScaleDown(src1[2], src1[5], src2[2], src2[5]);
const int W = RGBToGray(r, g, b);
dst[0] = (fixed_t)FixedYToW(r - W);
dst[1] = (fixed_t)FixedYToW(g - W);
dst[2] = (fixed_t)FixedYToW(b - W);
dst += 3;
src1 += 6;
src2 += 6;