bt709 coefficients for video constrained space

Original bt709 color space coefficients were full range yuv for higher
quality.  This change makes the coefficients use the video constrained
color space the same as bt601 which is 16 to 240 for Y and 16 to 235 for
chroma channels.

BUG=libyuv:639
TEST=libyuv unittests run locally
R=hubbe@chromium.org

Review URL: https://codereview.chromium.org/2367253003 .

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1620
+Version: 1621
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1620
+#define LIBYUV_VERSION 1621
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_

source/row_common.cc

@@ -1143,20 +1143,21 @@ const struct YuvConstants SIMD_ALIGNED(kYvuJPEGConstants) = {
 #undef YG
 
 // BT.709 YUV to RGB reference
-// *  R = Y                - V * -1.28033
-// *  G = Y - U *  0.21482 - V *  0.38059
-// *  B = Y - U * -2.12798
+//  R = (Y - 16) * 1.164              - V * -1.793
+//  G = (Y - 16) * 1.164 - U *  0.213 - V *  0.533
+//  B = (Y - 16) * 1.164 - U * -2.112
+// See also http://www.equasys.de/colorconversion.html
 
 // Y contribution to R,G,B.  Scale and bias.
-#define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
-#define YGB 32  /* 64 / 2 */
+#define YG 18997 /* round(1.164 * 64 * 256 * 256 / 257) */
+#define YGB -1160 /* 1.164 * 64 * -16 + 64 / 2 */
 
-// TODO(fbarchard): Find way to express 2.12 instead of 2.0.
+// TODO(fbarchard): Find way to express 2.112 instead of 2.0.
 // U and V contributions to R,G,B.
-#define UB -128 /* max(-128, round(-2.12798 * 64)) */
-#define UG 14 /* round(0.21482 * 64) */
-#define VG 24 /* round(0.38059  * 64) */
-#define VR -82 /* round(-1.28033 * 64) */
+#define UB -128 /* max(-128, round(-2.112 * 64)) */
+#define UG 14 /* round(0.213 * 64) */
+#define VG 34 /* round(0.533  * 64) */
+#define VR -115 /* round(-1.793 * 64) */
 
 // Bias values to round, and subtract 128 from U and V.
 #define BB (UB * 128            + YGB)