Re: luminanceToAlpha values in FEColorMatrix

On Mon, Sep 5, 2011 at 1:59 PM, Chris Lilley <chris@w3.org> wrote:

> On Sunday, September 4, 2011, 6:06:01 AM, Rik wrote:
>
> RC> I agree.I don't know what makes sRGB so special that it is the
> RC> default colorspace in SVG and used all over the spec.
>
> Because it was proposed (and accepted) as a standard default space, in the
> days when colour management was something that applied solely to high-end
> printing and Apple was trying to bring it to the desktop while other
> platforms were silent on the subject or in ostrich mode.
>
> So HTML 3.2 and 4 use it, and CSS 1 and 2. Thus, SVG did also.
>
> RC> Shouldn't SVG be color space agnostic (like PDF and Postscript)?
>
> Agnostic can easily translate to 'throw any value as at the screen and hope
> for the best'. That wasn't really good enough in 1980 and is certainly not
> good enough, even as a lowest common denominator, now. Consumer electronics
> has settled on sRGB while desktops and laptops (but not mobile, yet) has
> settled on ICC v.4 as a base capability.
>

Well, by defining it as the standard, you are limiting colors on devices
that have a wider gamut than sRGB.

Acrobat lets the user choose what his default space is. Why not let a SVG
renderer do the same? You could say in the spec that sRGB is a reasonable
default.
Maybe my disconnect comes from thinking about the destination/document
profile. Looking through the SVG spec, I can't find what colorspace the
colors are mapped to. Is it the device profile or sRGB?


>
> So sRGB as a default was a reasonable choice in 1996 and remains (arguably,
> has wider industry support) as a fallback for less capable devices in 2011.
>
> So I would disagree on 'agnostic'[1] as a goal, but if you rephrase to
> "shouldn't SVG allow other colour spaces as well" then I would be in full
> agreement. As long as there is a clear fallback.
>

Yes, SVG should support other color spaces natively.
There's been some discussion on spot and cmyk colors but I'm not sure if
there is a enough momentum to define it. Especially browser vendors might be
hesitant to implement this.



>
> RC>  There are several parts in the spec that talk about 'linear RGB' vs
> sRGB that are very confusing.
>
> Could you explain why it is confusing. The equations (in both directions)
> are given, and are fairly simple.
>

It's not so much about the equations.
Why is it needed? I don't believe that Adobe does this if you're just
drawing in RGB or CMYK. (We do play some tricks if you convert to a
different colorspace but I don't think that's relevant.)


>
> RC> Maybe there is some history here that I'm not aware of...
>
> Quite a bit, yes.
>
>
> [1] Either from Ancient Greek ???????? (agn?stos, ?ignorant, not knowing?)
> or from a- + Gnostic. Deriving (either way) from Ancient Greek ?- (a-,
> ?not?) + ???????? (gign?sk?, ?I know?).
>
> --
>  Chris Lilley   Technical Director, Interaction Domain
>  W3C Graphics Activity Lead, Fonts Activity Lead
>  Co-Chair, W3C Hypertext CG
>  Member, CSS, WebFonts, SVG Working Groups
>
>