W3C home > Mailing lists > Public > www-svg@w3.org > September 2011

Re: luminanceToAlpha values in FEColorMatrix

From: Rik Cabanier <cabanier@gmail.com>
Date: Sat, 3 Sep 2011 21:06:01 -0700
Message-ID: <CAGN7qDC2oRVpnm3ZdswV5FSnnPZt-hOgykueS6GZEbo_H_x=ww@mail.gmail.com>
To: David Woolley <forums@david-woolley.me.uk>
Cc: Dean Jackson <dino@apple.com>, public-fx@w3.org, www-svg <www-svg@w3.org>
I agree.
I don't know what makes sRGB so special that it is the default colorspace in
SVG and used all over the spec.
Shouldn't SVG be color space agnostic (like PDF and Postscript)?

There are several parts in the spec that talk about 'linear RGB' vs sRGB
that are very confusing.

Maybe there is some history here that I'm not aware of...

Rik

On Fri, Sep 2, 2011 at 3:56 PM, David Woolley <forums@david-woolley.me.uk>wrote:

> Dean Jackson wrote:
>
>   0.3086 red, 0.6094 green, 0.0820 blue
>>
>> Since sRGB is used throughout the SVG specification, and sRGB takes its
>> values from Rec 709, and Rec 709 seems modern (it's designed for HDTV), and
>> the values are really close to what is already specified, I suggest we
>> formally link to Rec 709 and use its values (a very slight change to current
>> implementations).
>>
>>
> sRGB is an engineering compromise, based on the behaviour of CRTs.
> Computing Y as a weighted average of gamma corrected values is very easy to
> do in simple analogue TV hardware, but doesn't one really want to have a
> formula that better reflect the subjective brightness to a human observer.
>  (I believe that, to a first approximation, the human eye can be modelled
> with a gamma curve of rather less than x^2.2., but these days, if you are
> using 24 bit colour, you could probably afford to store the whole lookup
> Y=f(R,G,B) lookup table, and for greater colour depths, you could
> interpolate.
>
> (I missed the start of this, but, if one is then going to use it as an
> alpha channel, one also needs to remove any remaining gamma correction.)
>
> I'm only subscribed to www-svg, so public-fx may be delayed or fail.
> --
> David Woolley
> Emails are not formal business letters, whatever businesses may want.
> RFC1855 says there should be an address here, but, in a world of spam,
> that is no longer good advice, as archive address hiding may not work.
>
>
Received on Sunday, 4 September 2011 04:06:32 GMT

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