adjust ubias to minimize error histogram centering error.

BUG=324
TESTED=TestFullYUV
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/37739004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1248 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1247
+Version: 1248
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1247
+#define LIBYUV_VERSION 1248
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

source/row_common.cc

@@ -960,40 +960,39 @@ void I400ToARGBRow_C(const uint8* src_y, uint8* dst_argb, int width) {
   }
 }
 
-// C reference code that mimics the YUV assembly.
+// YUV to RGB conversion constants.
 #define YG 19071 /* round(1.164 * 64 * 256) */
 #define YGB 1197 /* 1.164 * 64 * 16 - adjusted for even error distribution */
-
-// TODO(fbarchard): Adjusted U and V bias for even error distribution.
 #define UB -128 /* -min(128, round(2.018 * 64)) */
+#define UBB -16385 /* approx -round(2.018 * 64 * 128) */
 #define UG 25 /* -round(-0.391 * 64) */
-#define UR 0
-
-#define VB 0
+#define UGB 3200 /* -round(-0.391 * 64) * 128 */
 #define VG 52 /* -round(-0.813 * 64) */
+#define VGB 6656 /* -round(-0.813 * 64) * 128 */
 #define VR -102 /* -round(1.596 * 64) */
+#define VRB -13056 /* -round(1.596 * 64) * 128 */
+#define BB (UBB       - YGB)
+#define BG (UGB + VGB - YGB)
+#define BR (      VRB - YGB)
 
-// Bias
-#define BB (UB * 128 + VB * 128 - YGB)
-#define BG (UG * 128 + VG * 128 - YGB)
-#define BR (UR * 128 + VR * 128 - YGB)
-
+// C reference code that mimics the YUV assembly.
 static __inline void YuvPixel(uint8 y, uint8 u, uint8 v,
                               uint8* b, uint8* g, uint8* r) {
   uint32 y1 = (uint32)(y * 0x0101 * YG) >> 16;
-  *b = Clamp((int32)(BB - (v * VB + u * UB) + y1) >> 6);
+  *b = Clamp((int32)(BB - (         u * UB) + y1) >> 6);
   *g = Clamp((int32)(BG - (v * VG + u * UG) + y1) >> 6);
-  *r = Clamp((int32)(BR - (v * VR + u * UR) + y1) >> 6);
+  *r = Clamp((int32)(BR - (v * VR         ) + y1) >> 6);
 }
-
 #undef YG
 #undef YGB
 #undef UB
+#undef UBB
 #undef UG
-#undef UR
-#undef VB
+#undef UGB
 #undef VG
+#undef VGB
 #undef VR
+#undef VRB
 #undef BB
 #undef BG
 #undef BR

source/row_win.cc

@@ -24,30 +24,27 @@ extern "C" {
 #if !defined(LIBYUV_DISABLE_X86) && defined(_MSC_VER) && \
     (defined(_M_IX86) || defined(_M_X64))
 
-// YUV conversion constants.
+// YUV to RGB conversion constants.
 #define YG 19071 /* round(1.164 * 64 * 256) */
 #define YGB 1197 /* 1.164 * 64 * 16 - adjusted for even error distribution */
-
-// TODO(fbarchard): Adjusted U and V bias for even error distribution.
 #define UB -128 /* -min(128, round(2.018 * 64)) */
+#define UBB -16385 /* approx -round(2.018 * 64 * 128) */
 #define UG 25 /* -round(-0.391 * 64) */
-#define UR 0
-
-#define VB 0
+#define UGB 3200 /* -round(-0.391 * 64) * 128 */
 #define VG 52 /* -round(-0.813 * 64) */
+#define VGB 6656 /* -round(-0.813 * 64) * 128 */
 #define VR -102 /* -round(1.596 * 64) */
-
-// Bias
-#define BB (UB * 128 + VB * 128 - YGB)
-#define BG (UG * 128 + VG * 128 - YGB)
-#define BR (UR * 128 + VR * 128 - YGB)
+#define VRB -13056 /* -round(1.596 * 64) * 128 */
+#define BB (UBB       - YGB)
+#define BG (UGB + VGB - YGB)
+#define BR (      VRB - YGB)
 
 static const vec8 kUVToB = {
-  UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB
+  UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0
 };
 
 static const vec8 kUVToR = {
-  UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR
+  0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR
 };
 
 static const vec8 kUVToG = {
@@ -55,11 +52,11 @@ static const vec8 kUVToG = {
 };
 
 static const vec8 kVUToB = {
-  VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB,
+  0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB,
 };
 
 static const vec8 kVUToR = {
-  VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR,
+  VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0,
 };
 
 static const vec8 kVUToG = {
@@ -1475,12 +1472,12 @@ void RGBAToUVRow_SSSE3(const uint8* src_argb0, int src_stride_argb,
 
 #if defined(HAS_I422TOARGBROW_AVX2) || defined(HAS_I422TOBGRAROW_AVX2)
 static const lvec8 kUVToB_AVX = {
-  UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB,
-  UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB, UB, VB
+  UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0,
+  UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0, UB, 0
 };
 static const lvec8 kUVToR_AVX = {
-  UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR,
-  UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR, UR, VR
+  0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR,
+  0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR, 0, VR
 };
 static const lvec8 kUVToG_AVX = {
   UG, VG, UG, VG, UG, VG, UG, VG, UG, VG, UG, VG, UG, VG, UG, VG,