[cairo] Spot colors (and CMYK)

Bill Spitzak spitzak at gmail.com
Thu Feb 18 11:47:20 PST 2010

Andrea Canciani wrote:

> Actually all of the quartz surface/image creation functions have a
> colorspace parameter.

There is however a default value for this for screen windows and I have 
no idea what a non-default value produces. I can't even figure out 
whether this defines the space to convert *to* or *from*. Certainly from 
experiments it is obvious that it has no effect on what is stored in the 
buffers, even if it inverted perfectly the quantization of integer image 
buffers would mean images read back would differ.

> They are quite similar to what Adrian Johnson came up with when trying
> to add colorspace support to cairo (and tightly related to PDF
> design). This seems the right way to follow and is what I'll probably
> implement. I'll post the proposed extension to current API as soon as
> possible

Yes if the backend is designed to produce multiple color spaces, it can 
have a device-specific api to set this output color space. People also 
want to stick titles and html references in pdfs and Cairo has 
pdf-specific apis to do this.

What I do not want is some idea that the color space of the display 
screen can be changed.

> Andrea Canciani
> PS: I tried to get a few snapshot of my desktop with different color
> profile settings. I found amazing how well color management is handled
> by "Preview" (I used it to both grab and view the images). The images
> were automatically created with the ICC profile currently set on the
> screen (and it was attached to the image, too) and used as such (i.e.
> displayed correctly, not ignoring it). I realize that most of this is
> not done by Preview itself, but by Quartz and I think that the same
> should happen in cairo.

As far as I can tell messing with the color management on OSX changes 
all the displayed images the same. It does not attempt to correct a 
screen shot made with one setting to look that color when you change the 

I think instead the images are being tagged with a fixed color space 
that says "the default color space". This agrees with what I want, with 
the further attempt to nail this fixed color space down to sRGB.

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