[CSSWG] Minutes Color HDR Breakout 2025-04-09 [css-color-hdr]

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CSS Color HDR Breakout
======================

Require `H2 >= H1`? (Issue #11787)
----------------------------------

  - RESOLVED: Require strict inequality for H1 and H2

2.4 "two dynamic-range-limit-mix values" should be "two or more ..."
    (Issue #11694)
--------------------------------------------------------------------

  - RESOLVED: Allow single value, well defined

Auto value of dynamic-range-limit (Issue #11558)
------------------------------------------------

  - There was general agreement to add an auto value, but not yet
      agreement on how it should behave. Folks will keep thinking about
      the behavior and come back to this issue.

===== FULL MEETING MINUTES ======

Agenda: https://lists.w3.org/Archives/Member/w3c-css-wg/2025AprJun/0002.html

Present:
  Christoper Cameron
  Simon Fraser
  Chris Lilley
  Jeffery Yasskin

Chair: ChrisL

CSS Color HDR
=============

Require `H2 >= H1`?
-------------------
  github: https://github.com/w3c/csswg-drafts/issues/11787

  ccameron: This is to avoid a divide by zero
  <ccameron> the epsilon should only be used to color match (very
             exactly) with an image
  <ccameron> this feature is good enough without eps
  <ccameron> it's purely numerical
  <ccameron> can set to like 0.5 even
  <ccameron> the epsilon value is in the gain application color space
             (which is linear, and is either "base image" primaries or
             "alternate image" primaries)
  <ccameron> in practice, that's sRGB, P3 or Rec2020 primaries
  <ccameron> what's the gain application color space?
  <ccameron> primaries of the first space specified is most "normal"
             default

  RESOLVED: require strict inequality for H1 and H2

2.4 "two dynamic-range-limit-mix values" should be "two or more ..."
--------------------------------------------------------------------
  github: https://github.com/w3c/csswg-drafts/issues/11694

  <ChrisL> Most edits done, need to discuss about allowing a single
           value or not
  <ChrisL> WPT allows single value

  RESOLVED: Allow single value, well defined

auto value of dynamic-range-limit
---------------------------------
  github: https://github.com/w3c/csswg-drafts/issues/11558
  scribe: jyasskin

  ccameron: We probably won't agree on the default value. Having auto
            be browser-chosen and map to a single value ... maybe it's
            start on one state, and we'll eventually agree on something
            and be able to standardize that.
  ccameron: But I think I can't change several years of Chrome
            behavior, and good HDR doesn't need reduction, and the
            concern that HDR content will get mastered poorly if
            constrained by default.
  ccameron: I think we should have auto do what the browser wants, and
            provide the signal that the user left the default instead
            of explicitly asking for one of the options. Is that
            reasonable?

  simon: Apple doesn't have too much information. We want auto to be
         uniform for all elements. Ideally we don't want images+videos
         to have different behavior if 'auto' is applied to both, but
         we have historical behavior we might have to support.
  simon: Can't commit that auto will be the same for all elements.
         Don't want heuristics ... might decide full-screen will allow
         full HDR.
  simon: Don't plan any in-page heuristics like "image is next to text".

  simon: Question about HDR-CSS colors vs HDR images & video: are we
         agreed that the dynamic-range-limit property affects both box
         decorations and content?
  <jyasskin> <yes>
  ChrisL: We don't have syntax, and we're waiting for someone to do it,
          but we intend it to affect everything. If you want a
          particular thing, you should select it.
  simon: We do have a bug, but that's a bug. When people start
         specifying these colors, people might want to specify colors
         and replaced content separately.
  ccameron: Can specify different colors for different elements.
  simon: Videos have internal controls (??) which might want different
         color limits.
  ChrisL: I'm writing some tests.
  ChrisL: WPT is SDR & sRGB-only, but you can still test color mapping.
          Don't know how you'll get a headroom value.
  ChrisL: Does Apple have concerns?
  simon: Haven't digested the spec enough. Any concerns would be in
         terms of how HDR colors coexist with other content. To prevent
         annoying use.

  <ccameron> Proposed resolution: add "auto" value, which maps to
             browser-defined value (1 of the 3)
  ccameron: Suggest we sleep on this.
  simon: Think I'm OK resolving to add an 'auto' value, but not ready
         to say exactly how it behaves. Not ready to say it applies
         equally to images and video.

Received on Wednesday, 9 April 2025 22:52:00 UTC