Re: Pre-meeting Thoughts on HDR Canvas

On Wed, Jan 27, 2021 at 2:23 PM Lars Borg <borg@adobe.com> wrote:

> It is easy to assume that blending in gamma space is always undesirable.
>
> History tells a different story. Blending in non-linear space is common.
>
> For example, in Photoshop you can select to blend in linear or non-linear
> space.
>
> It’s a creative choice. It seems most users select the non-linear option.
>
> AFAIK video fades are typically in code space, not linear space.
>
> So it seems we should retain this option.
>
>
>
> Lars
>

Right, it is definitely an issue that content creators have gotten used to
living with.  From the developer's perspective though it can be haunting,
especially when working on apps that aim to be profile agnostic.  Of
course, the web dev community will figure out how to work around this, and
the complicated bits will be hidden deep in the guts of popular graphics
frameworks and game engines. But this will likely come with a performance
cost especially for 2D contexts.  On the other hand, if the canvas API
could provide additional levers to control this behaviour, then the browser
could leverage hardware acceleration features.


>
> *From: *Justin Novosad <junov@google.com>
> *Date: *Wednesday, January 27, 2021 at 7:59 AM
> *To: *Chris Lilley <chris@w3.org>
> *Cc: *"public-colorweb@w3.org" <public-colorweb@w3.org>
> *Subject: *Re: Pre-meeting Thoughts on HDR Canvas
> *Resent-From: *<public-colorweb@w3.org>
> *Resent-Date: *Wednesday, January 27, 2021 at 7:59 AM
>
>
>
> Thanks Chris for correcting me.
>
>
>
> I realize this is an old problem, but I think that adding HDR capabilities
> to canvas risks exacerbating it greatly because we will end up with
> inconsistent blending and gradient interpolation based on the canvas's
> working profile.
>
> For example, if a hypothetical app selects a canvas working profile to
> match the output device's capabilities, these behavior discrepancies risk
> being perceived as bugs and will be unpleasant to work around for web
> developers.
>
>
>
> On Wed, Jan 27, 2021 at 12:46 PM Chris Lilley <chris@w3.org> wrote:
>
>
> On 2021-01-27 18:32, Justin Novosad wrote:
> > The CSS and SVG specifications do not explicitly address the issue of
> > gamma-correct blending, but the examples in the CSS spec suggest doing
> > things the "wrong" way, which ignores gamma correctness.
>
> The SVG specification explicitly says that filer operations are in
> linear-light sRGB by default (with an option to change to sRGB, where
> speed is more important than getting the right result); and that all
> other operations are (sadly) in gamma-encoded sRGB by default (with an
> opt-in for linear-light sRGB).
>
> The CSS Compositing specification, sadly, requires operations in
> gamma-encoded sRGB. This choice was primarily driven by backwards
> compatibility with existing content; and secondarily with compatibility
> of blend modes, as popularized in Adobe Photoshop, which are also
> computed in gamma-encoded RGB spaces.
>
> CSS Compositing thus needs to add an opt-in for linear-light compositing.
>
> --
> Chris Lilley
> @svgeesus
> Technical Director @ W3C
> W3C Strategy Team, Core Web Design
> W3C Architecture & Technology Team, Core Web & Media
>
>