🚀 go-pugleaf

Hi

The new red book suggests that colours can be specified in CIE XYZ space
simply by parameterising the existing CIEBasedABC colour model with the
white point.  Like this

%%% Establish CIE XYZ space, Ref Manual p189-91 with the CCIR 
%%% recommended white point

[/CIEBasedABC <<
  /RangeABC [0 0.9505 0 1 0 1.0890]
  /RangeLMN [0 0.9505 0 1 0 1.0890]
  /WhitePoint [0.9505 1 1.0890]
>>]setcolorspace

This just sets the (X,Y,Z) coordinates for the white point and says that
all colour values must be in the range 0 to the white point.

Which would be used like this

0.7 0.27 0.03 setcolor

to get a nice red, for example. (Note that I cheated with this example by
making X+Y+Z=1, so I could read the coordinates off a standard xy diagram
like you see in any book on colour <grin>.)

Anyhow, this raises several questions which I had hoped someone here would
know the answer to:

A) The interpreter must store the CIE chromacity (xy) or tristimulus
(X,Y,Z) values for its inks internally. Indeed it must also store the
values for the secondaries too, since the (x,y) point of a secondary is not
on the line joining the (x,y) points of the two corresponding primaries.
*So* how do you get the interpreter to divulge these values?

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

C) what happens if you specify a coordinate that isn't even a colour? Like
X=0.7 Y=0.1 Z=0.2, which gives x=0.7, y=0.1 and is outside the flat edge at
the bottom of the 'tongue'. You will need to look at a diagram to udrestand
this, and I'm not going to attempt one in ascii!

Any answers are welcome, either email or post, and yes I will summarize any
answers in a later posting.

	Chris

PS Manufacturers of colour level2 PS devices are especially welcome to
reply! :)  Adobe is hereby extended a cordial invitation to provide an
authoritative answer.