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Re: Color formats

From: Chris Lilley <chris@w3.org>
Date: Sun, 07 Nov 1999 17:23:15 +0100
Message-ID: <3825A773.9DC6EB75@w3.org>
To: Tim Bagot <tsb@ox.compsoc.net>
CC: Style Sheet mailing list <www-style@w3.org>


Tim Bagot wrote:
> 
> On Sat, 6 Nov 1999, Garth Wallace wrote:
> 
> > There's one item, about allowing HSV/HSL notation
> > for colors. Why not CMYK? It would be very convenient
> > in @media print styles.
> 
> The problem with CMYK is that it is very device-dependent, far more so
> than RGB (or indeed HSV). What looks good on the author's printer could
> appear very different on another one.

Thanks Tim, for expressing this so clearly. Withthe wide variation in
CMYK parameters such as colorant, illuminant, substrate (reflectance)
spectrum, dot gain, press creep, and suchlike, it is very difficult to
use CMYK when the result is not aimed at a particular device in a
particular calibrated stste.

> The only real solution to this is to
> use a device-independent colour space (of which several exist);
> unfortunately, I suspect that colour management would be putting
> unreasonable demands on user agents.

Well, CSS2 (and CSS1) do demand correction for gamma as the absolute
minimum amount of color management. And they both use a measurable
definition of color, sRGB, which can be input to a CMS and output to
whatever device the user agent is running on.

> 
> I feel that, in general, very accurate colour should not be required for
> ordinary text, etc. 

Specification accuracy, and accuracy of reproduction required for
conformance, are two different things that should be clearly
distinguished here.

> Photographic images may well benefit from this, but
> they can be supplied in an image format which can carry the relevant
> information (e.g. PNG).

Yes, PNG can have a very short chunk added which says "this image is in
sRGB" or a rather long chunk added which says "this image conforms to
the following ICC profile". CSS2 (and CSS1) have the former capability
turned on all the time, and the latter capability may be available as an
option in later levels of CSS - providing thatthere is always a fallback
to sRGB for non-CMS-capable or minimally-CMS-capable user agents.
--
Chris
Received on Sunday, 7 November 1999 11:23:19 GMT

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