[ttml2] Change to Appendix Q.2

simontWork has just created a new issue for https://github.com/w3c/ttml2:

== Change to Appendix Q.2 ==
_Description:_

The gamma value used in item three of Q2 includes a psychovisual rendering for sRGB under reference conditions. The HLG signal does not include such an adjustment, therefore this gamma value should be 2.0 not 2.2. Uncorrected this error would result in pictures looking too dark in the mid-tones. A note is required to clarify that this gamma is intentional and not an error.

_Required change:_

The following equation:

**(r<sup>2.2</sup>,g<sup>2.2</sup>,b<sup>2.2</sup>) → (r,g,b)**

should be changed to:

**(r<sup>2.0</sup>,g<sup>2.0</sup>,b<sup>2.0</sup>) → (r,g,b)**

The note at the end of Q.2 should have the following text added:

**The gamma index 2.0 is intentionally different from gamma 2.2 specified in IEC/4WD 61966-2-1: Colour Measurement and Management in Multimedia Systems and Equipment - Part 2-1: Default RGB Colour Space – sRGB. The value 2.2 from the specification is specific to the viewing environment specified therein, and includes a psychovisual rendering adjustment for those conditions. This adjustment is not required for an HLG signal, which excludes display rendering.**

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/496 using your GitHub account

Received on Friday, 17 November 2017 13:47:32 UTC