bt709 coefficients for video constrained space

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

Committed: https://chromium.googlesource.com/libyuv/libyuv/+/c11e9b7fb7c03f3480e43faa9a906aba48fec466

[fbarchard1, 2016-09-27 21:17:35]

Description was changed from

==========
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
==========

to

==========
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
==========

[fbarchard1, 2016-09-27 21:17:35]

fbarchard@google.com changed reviewers:
+ sotaro.ikeda.g@gmail.com

[fbarchard1, 2016-09-27 22:12:43]

https://codereview.chromium.org/2367253003/diff/20001/source/row_common.cc
File source/row_common.cc (right):

https://codereview.chromium.org/2367253003/diff/20001/source/row_common.cc#ne...
source/row_common.cc:1151: #define YG 16320 /* round(1.000 * 64 * 256 * 256 /
257) */
These should now be same as bt601 to compensate for Y-16.  Instead of
subtracting 16 from Y, the values as multiplies as is, and then an add is done
after which removes the 16 * 1.164, and adds 0.5 for rounding.

// Y contribution to R,G,B.  Scale and bias.
#define YG 18997 /* round(1.164 * 64 * 256 * 256 / 257) */
#define YGB -1160 /* 1.164 * 64 * -16 + 64 / 2 */

[hubbe, 2016-09-28 19:02:15]

hubbe@chromium.org changed reviewers:
+ hubbe@chromium.org

[hubbe, 2016-09-28 19:02:16]

LGTM

Would be even better if the code could handle both full and limited range
content somehow.

[fbarchard1, 2016-09-28 19:15:47]

On 2016/09/28 19:02:16, hubbe wrote:
> LGTM
> 
> Would be even better if the code could handle both full and limited range
> content somehow.

The code itself can... this is the table that defines the rotation matrix.
I've only got matrix for YUV to RGB... should have same for RGB to YUV.
And would be good to expose the color spaces at a higher level somehow.
But short term, fewer options is better.  If we can all agree on bt.709 with
these coefficients, thats better than an option to do both.

[fbarchard1, 2016-09-28 21:31:09]

media code refers to this document on matrix used
http://www.equasys.de/colorconversion.html

[hubbe, 2016-09-28 21:42:29]

On 2016/09/28 21:31:09, fbarchard1 wrote:
> media code refers to this document on matrix used
> http://www.equasys.de/colorconversion.html

The color coefficients are correct (except for the 2.0) and "studio swing"
videos are much more common than the
"full range", so LGTM.

[fbarchard1, 2016-09-28 22:05:09]

On 2016/09/28 21:42:29, hubbe wrote:
> On 2016/09/28 21:31:09, fbarchard1 wrote:
> > media code refers to this document on matrix used
> > http://www.equasys.de/colorconversion.html
> 
> The color coefficients are correct (except for the 2.0) and "studio swing"
> videos are much more common than the
> "full range", so LGTM.

The 2.0 clamping is a problem... its off by 5% for blue.  I'll put more info in
the bug

[fbarchard1, 2016-09-28 22:07:48]

Description was changed from

==========
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
==========

to

==========
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

Committed:
https://chromium.googlesource.com/libyuv/libyuv/+/c11e9b7fb7c03f3480e43faa9a9...
==========

[fbarchard1, 2016-09-28 22:07:50]

Committed patchset #4 (id:60001) manually as
c11e9b7fb7c03f3480e43faa9a906aba48fec466 (presubmit successful).