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[csswg-drafts] [css-color] sRGB transfer curve outside 0.0 to 1.0 range

From: Chris Lilley via GitHub <sysbot+gh@w3.org>
Date: Sun, 10 Jul 2016 09:21:11 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-164707380-1468142467-sysbot+gh@w3.org>
svgeesus has just created a new issue for 

== [css-color] sRGB transfer curve outside 0.0 to 1.0 range ==
> The transfer function is undefined outside the range 0% to 100%.

Earlier levels of CSS expressed a vague hope that wider gamut colors 
could be expressed using sRGB and values less than zero, or greater 
that 1.0. This approach requires an extension of the transfer curve 
(there are several possible ways to do so, and the method uis 
undefined) and does not fit well with current industry practice which 
uses an appropriately large colorspace and only in-gamut values.

Thus, css-color-4 gives a better way to do the same thing (the color, 
lab and lch functions).

Out-of-gamut sRGB colors are poorly supported in current browsers and 
the clipping method is undefined (there are several possibilities, 
scaling of all color components towards the grey axis in an additive 
colorspace is the preferred method, while merely truncating one 
component and leaving any in-range components unchanged is the ugliest
 and the most widely implemented if clipping is done. Or, maybe the 
declaration is skipped or some color like black is returned.

Web compat needs to be studied - are there sites using out of gamut 
colors in sRGB and if so what behaviour are they relying on. I suspect
 that there are few such sites and the behaviour is browser dependent 
but would like to see data.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/288 using your GitHub 
Received on Sunday, 10 July 2016 09:21:18 UTC

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