Re: Pre-meeting Thoughts on HDR Canvas

On Tue, Jan 26, 2021 at 2:51 PM Joe Drago <jdrago@netflix.com> wrote:

> * The canvas' working profile / pixel format
>   * Determines luminance gamut / luminance range
>   * Determines blending
>   * Determines precision (banding)
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I've only been following this discussion sporadically, so I am sorry if
this comment is redundant.

Though the canvas working profile determines the color space that is used
for blending, the profile's* transfer function should not affect blending*
because most blending op arithmetic has a baked-in assumption of
linearity.  Historically implementations have been performing linear
blending ops on gamma encoded color values, which is not great.  Fixing
this obviously creates a challenge for backwards compatibility of legacy
(SDR) content, but for HDR we have a blank slate and could take this
opportunity to do things right.   FWIW OpenGL has the same flaw, and faced
the same SDR backwards compat issue, which was solved by making the correct
behaviour "opt-in" with the EXT_sRGB extension. Something similar could be
considered for canvas.

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