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Re: [csswg-drafts] [css-color] Separation / DeviceN color support (#2023)

From: Chris Lilley via GitHub <sysbot+gh@w3.org>
Date: Tue, 31 Mar 2020 16:30:52 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-606736167-1585672250-sysbot+gh@w3.org>
Mike, thanks for helping me understand the complexities and constraints of PDF as a rendering target.

> PDF is likely to be the only target media that doesn't immediately collapse these to RGB, and PDF requires that a) the inks defined in any custom color-profile are defined using process colors, and b) that the same color-profile is use for all inks. The syntax I proposed reflects this.

So to help me understand - suppose that there weren't any standards for 7-color printing and I was inventing [FOGRA55](https://www.fogra.org/index.php?menuid=782&reporeid=524&getlang=en) by creating tests in PDF to be printed. So Basically I start with [FOGRA51](http://www.color.org/chardata/fogra51.xalter) CMYK and then add three spot color inks:

  * Green: "Pantone Green C" which is lab(57.7% 77.2 0.2) 
  * Orange: "Pantone Orange 021C" which is  lab(60.8% 65.7 85.1)
  * Violet: "Pantone Violet C" which is lab(18.8% 54.5 -69.5)

I want those separations printed with the actual spot inks, and furthermore I can't express those as CMYK process colors because they are outside the gamut of my CMYK set (which is why they are added in the first place, to extend the gamut).

The only way I can wrap my head around that is to think that PDF requires the process color equivalents in the same way that CSS has optional fallback colors for device-cmyk - so that it can do something with them when a blend is required. But only as a fallback, the actual spot colors will be used when it prints, right? Otherwise there would be no way to apply spot "colors" like metallics, varnishes, embossing and folding.


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Received on Tuesday, 31 March 2020 16:30:55 UTC

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