Re: Adding support for HDR headroom in ScreenDetailed

Thank you!

I've updated the explainer with this section
<https://github.com/ccameron-chromium/ColorWeb-CG/blob/master/screen_hdr_headroom.md#example-use-cases>
outlining the two main use cases (custom tone mapping, and ensuring
accurate color grading).

I actually have a bunch of demos that depend on this (in various prototype
forms). Probably the best one is this gainmap demo
<https://ccameron-chromium.github.io/webgl-examples/gainmap-viewer.html> (it
requires experimental web platform features to be enabled), in which the
custom tone mapping shader will adapt to the selected headroom (called "HDR
to SDR ratio" in the app), which can be set automatically using this
feature.





On Tue, Jul 1, 2025 at 10:07 PM Mike Wasserman <msw@chromium.org> wrote:

> FWIW, I generally support enhancing ScreenDetails with HDR info about the
> display.
> Chris, can you add a simple example in the explainer, showing how
> this resolves web developer requirements, which are otherwise unmet?
>
> On Tue, Jul 1, 2025 at 5:50 AM Christopher Cameron <ccameron@google.com>
> wrote:
>
>> 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.
>>>
>>>
>>>