Re: Adding support for HDR headroom in ScreenDetailed

Please let me know if there are any concerns with this proposal!


On Mon, Jun 23, 2025 at 7:33 PM Christopher Cameron <ccameron@google.com>
wrote:

> Hello Second Screen WG (and ColorWeb-CG as FYI)!
>
> The HDR headroom of a screen is a core parameter for how HDR content is
> rendered (see this description in CSS HDR
> <https://drafts.csswg.org/css-color-hdr/#introducing-headroom>). Advanced
> applications may want to perform custom tone mapping using this parameter.
> This is another brick in the HDR canvas proposal
> <https://github.com/w3c/ColorWeb-CG/blob/hdr_canvas_r2/hdr_html_canvas_element.md> that
> has been slowly making progress.
>
> The short version of the proposal is: Add the screen's HDR headroom
> parameter to ScreenDetailed. It is a potential fingerprinting vector, so
> ScreenDetailed is a better fit than Screen. It can also fluctuate rapidly
> (e.g, when the screen brightness changes) and independently of other screen
> properties, and so it gets its own "on change" event, separate from the
> other screen properties.
>
> Please see below for the fully fleshed out proposal:
>
>    - Issue <https://github.com/w3c/window-management/issues> on
>    window-management API
>    - PR <https://github.com/w3c/window-management/pulls> on
>    window-management API
>    - Explainer
>    <https://github.com/ccameron-chromium/ColorWeb-CG/blob/screen_hdr_headroom/screen_hdr_headroom.md>
>
> This has been shipping behind a flag for several years (although with some
> slight API differences, which have been ironed out to better fit the CSS
> HDR model). Now that HDR content is getting to be much more common, there
> have been several requests to get this out from behind the flag.
>
>
>