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Re: [csswg-drafts] [css-color] Generic Transform Function for RGB Color Spaces (#4488)

From: Mike Bremford via GitHub <sysbot+gh@w3.org>
Date: Wed, 13 Nov 2019 16:38:07 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-553484500-1573663086-sysbot+gh@w3.org>
Each of these spaces is completely defined by an ICC profile. So conversion to or from any of these spaces is going to be done by the ICC code, rather than by doing the maths by hand. I don't think there's any value in trying to reproduce the ICC profile in CSS.

That said, in the PDF world defining ColorSpaces *without* reference to an ICC profile is extremely common. It's not used for RGB as you've done here, but to define custom separations - a single separation is often called a "spot color", but they can be combined with other custom separations or the normal process colors (cyan, magenta, yellow and black) to form what PDF call "DeviceN" ColorSpaces.

I attempted to tackle this in #2023.

The ability to define custom separations is absolutely critical for any CSS to PDF engine. It's not a nice-to-have, and it's not something that can be done with ICC profiles. All products I'm aware of (Prince, Antenna House, RealObjects, our existing Report Generator and our new under-development engine all have a method for this, many loosely based on the `rgb-icc` function defined in https://www.w3.org/TR/xsl11/#expr-color-functions, but personally I don't think that approach is very well thought out. I'd really like to see it standardised.

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Received on Wednesday, 13 November 2019 16:38:09 UTC

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