Re: Pre-meeting Thoughts on HDR Canvas

Common and desirable are not necessarily correlated. If non linear blending is the application default, most users are “choosing” it by never making a conscious decision. I’m having trouble finding cases where non linear blending is desirable or produces a better result, for any definition of “desirable” or “better”…

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Lea Verou ✿ http://lea.verou.me ✿ @leaverou

> On Jan 28, 2021, at 00:38, Leonard Rosenthol <lrosenth@adobe.com> wrote:
> 
> 
> I would say that pretty much every content authoring tool – be it graphics (Photoshop, Inkscape, Scribus) or documents (MSOffice, GDocs, PDF, etc.) uses gamma/non-linear blending – though also in SDR.  To change that in the web space (at least for SDR content) would also require a change of all of those authoring tools or users won’t be able to author content that matches.
>  
> I do agree, however, that in the context on HDR content it may well make sense to consider alternatives since the authoring isn’t there yet…. Provided that we fully describe a mixed SDR/HDR stack and how compositing would work in such a scenario – especially when multiple colorspaces are also involved…
>  
> Leonard
>  
> From: Lars Borg <borg@adobe.com>
> Date: Wednesday, January 27, 2021 at 2:23 PM
> To: Justin Novosad <junov@google.com>, "chris@w3.org" <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 2:23 PM
>  
> 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
>  
> 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
> 
>