Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "David Wroblewski" 
<dawroblewski@y...> wrote:
> --- "ccolbertbw" <ccolbert@u...> wrote:
> >   Remember that this is using QTR and gimp-print. The 
> >   final files produced by Roy's calibration procedure 
> >   just tell the driver how much ink to put out for each 
> >   pixel value. These are just text files, so, it is easy 
> >   enough to just replace all values with zero for all 
> >   inks except the one of interest. 
> 
> Aha. Fiendishly clever. So one could produce profiles called,
> "JustC", "JustY", "JustM", "JustK", and so on, which direct 
> QTR to use the one ink, then print a grayscale ramp.
> 
> I also see your point that running a calibration pretending 
> there is only 1 ink is a good quick method.
> 
> I need to spend some time doing some basic exercises, such as
> setting up a curve file that prints each ink, another that prints 
> them all just like the Epson driver, etc, before I understand 
> this completely. I know that's somewhat academic--I could just 
> start printing with the curves I have now, having corrected the
> constant in the code. But I would like to understand how this all
> works a little better.
> 
> Thanks, that was helpful.
> 
> -david

David,

The calibration page inkpattern.psd just makes it easy to see the inks
separately.  So it basically gives you the "JustC", "JustY", "JustM", "JustK"
on one page.  The idea of calibration is to express each lighter ink as a
percentage of the darker ink.   Well the dots are exactly analogous,
you want express a smaller dot as a percentage of the larger dot. 
Underlying its really just a volume measurement of the droplet of
ink -- the in this case the small dot is 45% of the volume of the large
dot.  Since we can't actually see or measure the individual dots, the
method I've been using is matching the densities.  I do a patch of
100% coverage using just the small dot, then I see what percent
coverage using just the large dot is necessary to get the same density 
on the paper.  I've carried it a little further by doing a whole step
wedge for each dotsize and trying to fit the whole curve together.

Unfortunately, doing a calibration page for the dots is a little more 
complicated, but all in all its the same principle.  If you interested in
the gory details of this I'd be glad to share it offline.

Roy