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Re: [css4-color] unclamped values for RGB

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 15 Jun 2012 12:24:51 -0700
Message-ID: <CAAWBYDA0eXLG92nzyaFsd8SbZrqPYOTO_837i8NeF-gvEFHzGA@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: www-style list <www-style@w3.org>
On Fri, Jun 15, 2012 at 12:07 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> currently the CSS color allows color values larger than 1 and smaller than 0
> (see the bottom section
> of http://www.w3.org/TR/CSS21/syndata.html#value-def-color). I'm unsure if
> anyone has actually implemented this.
>
> The spec currently defines that all non-image colors are defined in sRGB
> which is a simplistic profile. It's gamma correction + a simple translate
> function. Clamping to [0..1] is part of the definition
> (see http://en.wikipedia.org/wiki/SRGB)
>
> The problem with this is:
> a. This is breaking the profile math.  Are all out of gamut colors possible
> or only a subsection?
> b. Colors with out of gamut colors will display different than they print
> c. What if we want to improve color on the web later on? sRGB used to make
> sense but current displays are capable of a wider gamut (ie Super OLED)
> which currently goes unused or abused to show colors that are too vibrant.
> New displays will probably have table based profiles where unclamped input
> makes no sense.
>
> I think this feature should be dropped and replaced with something that is
> colorimetrically correct. This could be Lab or the ability to specify what
> profile the author intends to use (or both :-0)

The intention (possibly not properly captured in the draft) is that
the rgb() function specifies a color in an unclamped sRGB space.  The
browser can then clamp the components to restrict the color to the
gamut of the output device.

~TJ
Received on Friday, 15 June 2012 19:25:40 GMT

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