[cairo] Spot colors (and CMYK)

Chris Murphy lists at colorremedies.com
Thu Feb 18 18:42:19 PST 2010

On Feb 18, 2010, at 10:56 AM, Bill Spitzak wrote:

> Apple and Adobe provide a FIXED conversion from sRGB to the display.

Define "fixed conversion from sRGB to the display" please. I do not know what you mean by this, in particular by the word "fixed".

And actually in Adobe applications, the source space is user and document definable. By default, if a TIFF with embedded ProPhoto RGB profile is opened in Photoshop, or placed in InDesign, that profile is used as the source, and sRGB never comes into play.

> This is the REAL solution and is exactly what everybody wants. Please 
> look, there are apis in Cocoa to draw images that do not provide a "cms" 
> but they WORK and you can actually adjust your screen to produce the 
> correct color, and every program agrees!

Adjust the screen how? You mean through the display's OSD? That is completely f|cked up if that's what you mean. This sort of screw up the display to make the image look right is a workflow that was rejected over a decade ago for professional workflows.

> Yes there are apis to provide a cms so they can concatenate it with 
> their internal one. However this is the PROBLEM, not the solution.

Who is "they" and "their"? What is "internal one"? Why is this a problem?

> We 
> certainly never use this, but from our experience with other cms 
> libraries I can be pretty certain there are a million bugs with this 
> concatenation so that the result never matches what happens if I convert 
> to the fixed sRGB space and send that, and this means images do not match.
> Believe me I am very interested in emulating how Apple is doing things, 
> and that I think your ideas are EXACTLY OPPOSITE this.

Many of Apple's own applications ask the OS what the current system profile is (the current display profile), which in default cases is a profile built on the fly from the display's EDID. The app then submits data for display, tagged with this display profile, to Quartz. Since source=destination, there is no conversion.

Any application which does not explicitly set a profile for data to be displayed (or printed) is assumed to be Generic RGB on OS X 10.5 and older, and sRGB on OS X 10.6 and later. From that space, it is converted to the system profile (the profile for the display, or DisplayRGB).

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

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