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Re: [css4-color] Make the r/g/b components be <number> rather than <integer>?

From: Rik Cabanier <cabanier@gmail.com>
Date: Fri, 15 Jun 2012 20:54:47 +0200
Message-ID: <CAGN7qDDeXbNeyHaRJkbAnU8iyVbu0Kf=e2B4VxYhHDMVm6WYGw@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: Boris Zbarsky <bzbarsky@mit.edu>, www-style@w3.org
On Fri, Jun 15, 2012 at 8:41 PM, Tab Atkins Jr. <jackalmage@gmail.com>wrote:

> On Fri, Jun 15, 2012 at 11:24 AM, Rik Cabanier <cabanier@gmail.com> wrote:
> > sRGB 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)
> > I can see how this would make it tempting to just remove the clamp so you
> > can get to XYZ that is outside of the regular gamut.
> >
> > 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 negative input
> > make no sense.
> >
> > I think point c is most important.
>
> I'm not sure how any of this is relevant to either the original
> discussion in this thread, or the tangent topic that has split off.
>
> The rgb() function allows unrestricted integers (and percentages).
> UAs may clamp the arguments to whatever gamut the output device
> supports.  This might be [0-255], or it might be a larger range if
> you're using a higher-gamut display or a printer. It could even be a
> lower range on some printing devices.  So, this is all undefined by
> CSS and up to the UA - it's a quality of implementation issue.


It is relevant because it's specified in the spec. See the bottom section
of http://www.w3.org/TR/CSS21/syndata.html#value-def-color:

"All RGB colors are specified in the sRGB color space"

sRGB is clipped to [0 1]

The sentence that is causing the most confusion for me is:

*"*Other devices, such as printers, have different gamuts than sRGB; some
colors outside the 0..255 sRGB range will be representable (inside the
device gamut), while other colors inside the 0..255 sRGB range will be
outside the device gamut and will thus be mapped."

Boris believes this means that <0 and >1 values are allowed
Received on Friday, 15 June 2012 18:55:17 GMT

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