[cairo] Subtractive API, part 0

Chris Murphy lists at colorremedies.com
Sat Jan 30 12:23:53 PST 2010

On Jan 30, 2010, at 4:59 AM, Jon Cruz wrote:
> Color management of *some* sort is required. For many situations, however, the W3C was able to solve the need by simply stating "all RGB values are in the sRGB colorspace". No need for conversions, libraries, etc.

By defining all content in sRGB, they are effectively demanding all user agents (browsers) support full display compensation, assuming all elements are sRGB and must be converted to displayRGB. The assumption that displays are even close to sRGB is flawed. Display compensation is required to get any consistency between browsers.

The problem is that the browser doesn't have control over plug-in content. It can't color manage that. I guess the plug-in acts as its own user agent, and interfaces with the OS/window server directly, rather than passing content through the web browser in a way such that the browser could color manage the content.

Anyway, things are a bit of a mess between Windows and Mac OS land, because on OS X 10.6 the window server assumes sRGB for untagged content and will color manage it. So it almost seems to obviate the effort Mozilla has put into a cross platform color management engine into FireFox.

But the W3C, when it comes to the CSS 2 and 3 specs, is clueless about how things actually work. I'll reference the CSS2 version here, which is identical in CSS 3.


It's utterly ridiculous.

> A simple change in documentation was sufficient in many areas. If things stay there, then nothing further has to be done. However, if one needs to go in and out of things, then things should be converted in a predictable manner. There are simple ways that Cairo can be updated to handle more than RGB. However, if broken shortcuts are taken, then implementers, maintainers and users of Cairo will have to suffer with any poor decisions for quite some time to come. I'm fairly certain we all just want to find a minimal solution that will be sufficient. But again, I'm pretty sure that "let me throw random numbers in, and I don't care what comes out days or weeks later" is a route that is best to be avoided.

Yeah I agree completely with this. The industry has been there, done it, and it was painful. We're still dealing with those consequences to a great degree.

The actual color of a spot color itself can change over time. They do get redefined. And they don't get version numbers for us to tell.

Chris Murphy
Color Remedies (TM)
New York, NY
Co-author "Real World Color Management, 2nd Ed"

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