Digital BW, The Print

Steve Kale wrote:

> 3.  I'd like to understand why linearisation is best done with respect to L*
> and not XYZ_Y which is where the scaling is done.  This obviously requires
> the first item to be understood.  I would guess it has something to do with
> the linearity of L* as a concept and ease of interpolation but then on that
> I am just guessing.

I find something along those lines intriguing as well. We have 
discussed the Epson Colorbase calibration/linearisation. Jon 
Cone's curves/profiles for K7 and QTR have been discussed. For 
some time I wonder whether a linearisation in the strict sense 
of what is done in RIPs is actually used by both Epson and 
Jon. Is there something gained by keeping the natural dotgain 
curves etc of the Epson printers and build the curves or the 
perceptual right on them instead of linearising the printers 
first and then applying the perceptual curves/profiles ? 
Calibrating the printers to a standard still could respect 
that natural behaviour while it could also address the issues 
that do not deliver a better result.  But that doesn't make it 
a linearisation.

In RIPs there are choices that work at the level of 
linearisation like ink limiting and the CMY split etc. So I 
can understand that there's an extra level added based on a 
straight model. It still may be easier in color mixing control 
than any other model, in quad printing things are quite 
different though. In QTR linerisation is available too but 
there are ways like adapting the target values to get more a 
kind of a calibration than a strict linearisation. I might be 
far off-course but I have always wondered how Epson does it in 
the driver and Jon's messages made me curious too.

                    --
           Ernst Dinkla


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