Which display is the viewer on, and how much HDR headroom does it have?
(PROTOTYPE, ?hdr.)
Two sources, best first:
Measured. Chromium's Window Management API carries the screen's live
headroom on ScreenDetailed — hdrHeadroom in STOPS (the CSS HDR model)
and the older highDynamicRangeHeadroom as a plain MULTIPLE (measured on
a MacBook Pro: 2.667 and 6.35, and log2(6.35) = 2.667). Behind
--enable-experimental-web-platform-features as of Chrome 155, and only
after the window-management permission, which prompts — so it is used
when already granted, or after an explicit "Detect Display" click.
Model knowledge. Without a measurement, identify the panel from what
the page can see: the display label (the monitor's EDID model name,
e.g. M28U; permission-gated too), the GPU (WebGL's unmasked renderer
names the Apple chip), the platform and the screen geometry, then look up
a CONSERVATIVE headroom. Conservative because overshooting the real
headroom lets the OS clip the brightest detail, while undershooting only
leaves range unused — and no table knows the brightness setting, which
moves macOS EDR headroom several-fold.
Which display is the viewer on, and how much HDR headroom does it have? (PROTOTYPE,
?hdr.)Two sources, best first:
ScreenDetailed—hdrHeadroomin STOPS (the CSS HDR model) and the olderhighDynamicRangeHeadroomas a plain MULTIPLE (measured on a MacBook Pro: 2.667 and 6.35, and log2(6.35) = 2.667). Behind--enable-experimental-web-platform-featuresas of Chrome 155, and only after thewindow-managementpermission, which prompts — so it is used when already granted, or after an explicit "Detect Display" click.label(the monitor's EDID model name, e.g.M28U; permission-gated too), the GPU (WebGL's unmasked renderer names the Apple chip), the platform and the screen geometry, then look up a CONSERVATIVE headroom. Conservative because overshooting the real headroom lets the OS clip the brightest detail, while undershooting only leaves range unused — and no table knows the brightness setting, which moves macOS EDR headroom several-fold.