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Re: [csswg-drafts] [css-color-4] Clamping of color values (#3845)

From: Chris Lilley via GitHub <sysbot+gh@w3.org>
Date: Wed, 21 Oct 2020 17:58:58 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-713755672-1603303137-sysbot+gh@w3.org>
> The specification doesn't say how out-of-range values for profiled colors are handled. Are they clamped to their valid range or does an out-of-range value make the color invalid?

The specification now defines this. 

For custom colorspaces, defined by an ICC profile, specified out  of range values are simply clamped to the valid range at computed value time. This is because the ICC profile will not allow the out of range values as input, so this is all that can be done.

For predefined colorspaces, which have a mathematical definition of the transfer function, specified out  of range values are gamut mapped using a relative colorimetric intent, at used value time.

A new section describing relative colorimetric chroma reduction with speculative clamping will be added as an appendix.

Handling of specified values which are in gamut for the specified colorspace, but out of gamut for the display device, will also be covered in the gamut mapping section. Again, relative colorimetric will be used.

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