[csswg-drafts] [css-color-hdr-1] Compositing SDR in HDR outputs (#5323)

simontWork has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-color-hdr-1]  Compositing SDR in HDR outputs ==
Care must be taken to ensure any transform defined is robust, works for all inputs and does not greatly adjust the perceived image.  For example, a transform cannot simply scale SDR images in linear colour space, as the increased brightness and, if composited with HDR video, the presence of specular highlights will affect the perception of shadows and midtones - a perceptual gamma adjustment is required.

Furthermore, there are 2 transform routes available:

1. "Display Referred" - mathematically apply the BT.1886 EOTF to give linear output screen light, scale brightness and map into the target gamut, perceptual correction, mathematically apply the Inverse HDR EOTF to get the HDR signal
2. "Scene Referred" - mathematically apply the Inverse BT.709 OETF to give linear input camera sensor light, scale brightness and map into the target gamut, perceptual correction, mathematically apply the HDR OETF to get the HDR signal

For this application, I think variant 1 (which visually matches the displayed signal - as closely as possible) is the correct one to use.  By carefully choosing the parameters of the SDR and HDR EOTFs, we can simplify the transform and achieve a very close match. 

Further information is given in ITU-R BT.2390-8: https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2390-8-2020-PDF-E.pdf


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5323 using your GitHub account

Received on Tuesday, 14 July 2020 21:51:17 UTC