Re: Adding support for HDR headroom in ScreenDetailed

Hello Second Screen group!

Is there anything left to do before we merge the PR
<https://github.com/w3c/window-management/pull/150> for this issue
<https://github.com/w3c/window-management/issues/149>?

Thank you!


On Tue, Aug 26, 2025 at 4:07 PM Kostiainen, Anssi <
anssi.kostiainen@intel.com> wrote:

> Hi Christopher, All,
>
> Thank you for the HDR headroom proposal — it’s on the Second Screen WG’s
> WIP TPAC agenda:
>
> https://github.com/w3c/secondscreen-wg/issues/13
>
> WG participants - please review the proposal and provide feedback via GH
> prior. See the links provided by Christopher for the issue(s), PR and
> explainer.
>
> Color on the Web CG participants at TPAC are welcome to join us for this
> discussion.
>
> Thanks,
>
> -Anssi (Second Screen WG/CG co-chair)
>
>
> On 23. Jun 2025, at 20.33, 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.
>
>
>
>