RE: Agenda, TPAC 2019 ColorWeb CG Meeting.

Hi all,

I've commented in line.

-----Original Message-----
From: Chris Lilley <> 
Sent: 16 September 2019 09:57
Subject: Agenda, TPAC 2019 ColorWeb CG Meeting.

I had hoped that the ICC white paper on HDR with ICC would be available for discussion by this community group. Alas, that document does not yet have consensus within ICC so has not yet been published. Once it is, I will send a link to this CG for discussion.

Topics which would be particularly useful to discuss:

* Working Colorspace in CSS Color 4

For Web compat, things like compositing, gradients, anti-aliasing, and general color interpolation defaults to sRGB. This is not a linear space, so the results of computations are wrong. A new CSS property, working-colorspace, would allow this to be altered. This is particularly needed if any element is in a wider gamut colorspace.

[>>]  There may also be a need to be careful in which colour space you choose to work.  For example, neither CIE Yxy or CIE Yu'v' are linear in terms of hue, so a simple desaturation towards the white point will cause a hue shift in these spaces.  

* HDR and the Web, compositing SDR with HDR

Typical use cases include showing some information (subtitles, actor bio as a Web page) composited on top of HDR video. HDR (at least in PQ
encoding) uses absolute luminance, so where should sRGB white be placed? 
Clearly not at 80 nits, clearly not at 4000 nits or whatever the display is capable of for small hilights, and probably not at 1200 nts or whatever full-screen value the display is capable of. How should that work with HLG? What is the influence of scene metadata on this compositing?

[>>] ITU-R BT.2408-2 states "Graphics White is defined within the scope of this Report as the equivalent in the graphics domain of a 100% reflectance white card: the signal level of a flat, white element without any specular highlights within a graphic element. It therefore has the same signal level as HDR Reference White, and graphics should be inserted based on this level." 
[>>] For PQ this is defined as 58% and for HLG 75%.  If you display those signals on a PQ monitor or a 1000cd/m^2 HLG monitor it comes out at 203 cd/m^2.  On different brightness HLG monitors, the HLG adaptive system gamma implemented in the screen will maintain the perceptual contrast without any requirement of metadata.

* Image formats for HDR

Still images, such as stills from a movie or HDR photography, need to be displayed on the Web. Ideally, W3C would not develop a new format but use an existing, open, widely implementable one.

[>>] Indeed.  We would like to see a standardised graphics format.  PNG with an ICC profile could be a starting point. Does industry need a floating point format to allow for heavy editing which could cause banding in a integer-based system?

Simon Thompson 
Senior R&D Engineer

BBC Research & Development

Received on Monday, 16 September 2019 09:56:11 UTC