🚀 go-pugleaf

In article <4566@m1.cs.man.ac.uk> lilleyc@cs.man.ac.uk (Chris Lilley) writes:
>A) The interpreter must store the CIE chromacity (xy) or tristimulus
>(X,Y,Z) values for its inks internally.

This information is not represented directly, since inks typically do not
mix as color theory would predict. Instead, the calibration is embodied in
a color rendering dictionary. In the red book, see section 6.1, "CIE-Based
Color to Device Color". This mechanism provides substantial control over the
conversion from CIE values to device colorants, optionally including a full
3-D lookup table.

Each color printer has one or more default color rendering dictionaries
built-in. How this calibration was performed is not documented and in some
cases is proprietary to the printer manufacturer. There are companies whose
business is to provide tools and techniques for color calibration.

>B) what happens if you specify a colour that is outside the printer gamut?

This is under the control of the gamut mapping function, which is part of
the color rendering dictionary. This is where transformations such as gamut
compression, white point matching, clipping, and certain other operations
occur.

>C) what happens if you specify a coordinate that isn't even a colour?

I imagine the gamut mapping function will treat it as out-of-gamut and will
clip it, but this depends on the contents of the color rendering dictionary.
Once again, the PostScript language provides general mechanisms for color
conversion, but it does not prescribe policies to be applied in specific
cases.
-- 
Ed Taft      taft@adobe.com      ...decwrl!adobe!taft