[cairo] Spot colors (and CMYK)

[Bill Spitzak]

Jon Cruz wrote:

> Cairo needs to emit proper CMYK+spot details to the PDF.
> 
> Cairo *should* at the same time be able to 'preview' to an RGB display.
> 
> If that preview does not have ANYTHING to do with the spot color specified, then most even semi-profesionals will laugh their heads off at Open Source and dismiss such software as mere toys.

This sounds completely impossible. It sounds like you want composites in 
Cairo where some of the input is a spot color to exactly reproduce 
whatever effects the overprinting and mixing of the ink does on the printer.

I do not believe sufficient information is provided in cms descriptions 
for Cairo to produce a correct simulation color for any mixes. I also do 
not believe that anything, including OSX, does anything remotely 
resembling this.

The only plausable way I see for the display to be "accurate" is if it 
uses cms to reproduce the resulting composite on the printer. However 
this is certainly not what is wanted for spot colors, even if 100% spot 
color is detected and produces the desired ink, the antialiased pixels 
around the edge would be replaced with some simulation with the CMYK inks.

What I propose instead is that the program provide a "simulation" of the 
spot color in RGB (or in any normal color space if the proposed color 
space api is added). It is the program's responsibility to make this 
preview "accurate". This color is converted to the destination space and 
mixed there, while the backend (provided it understands the spot color) 
also keeps track of the resulting contribution of the spot color to the 
output pixels. When it finally prints the backend prints the desired 
amount of spot color, and perhaps some other inks to make up for 
overprinted colors.