Digital BW, The Print

> From: Ernst Dinkla <E.Dinkla@...>

>> 
> I know that the profiles are generic and that the underlying (custom)
> linearisation per printer/inkset should take care of a basic layer to
> use the generic profiles on top off. That it is still a compromise is
> also correct and custom profiling on top of a custom
> ink-limited/linearised-ink/paper/resolution set printer should be
> better, especially as the Dmax + the white point per printer/paper could
> vary and the generic profile will not adapt to that. On the other hand
> we shouldn't forget that many do not have the extra hardware to get the
> best custom calibrated and profiled output. So a bit more choice in
> generic profiles may be good for them while QTR should develop to even
> better control where possible.


I guess people could share profiles for a particular printer/paper/ink
setup.  I guess I would think it easier in the long run if we didn't have to
kep coming back to source if, say, MIS released a new and improved Eboni ink
or a new printer was released.  Roy does enough as it is....


> 
> Another thing that could be added to the B&W profiling software is the
> possibility to use data from 3 readings, either from 3 targets printed
> or from 3 readings from the same target. Increasing the number of
> greyscale steps in the target may give less gain in precision than
> multiple readings from more targets. Depends on the accuracy of the
> instrument, the handling and the software interpretation. To be honest
> producing a 256 step target goes beyond the capacity of many printers I
> think and what has to be done afterwards in getting a profile from so
> many shades may be worse as a result.

It is actually very easy to read even 256 patches with Quickread.  It takes
very little marginal time.  If the patches are shuffled (as my test target
is) an Eye One can get good readings but I agree there is a potential issue
there.  I expect measurement devices to continue to improve.  As to the
printer capability (ie separation), perhaps that is actual.  I guess the
more observations going into the kTRC tag the more likely you are to iron
out issues in the original linearization (eg black only is woefully
non-linear).  As for multiple readings or multiple prints and measurement of
a test chart, this is likely best left up to the user - the data can be
easily averaged prior to being read into the ICC profile generator.


>What would be interesting is an
> iteration feature, where a new target printed with the custom
> linearisation + custom profile delivers data that can be added to the
> profile for fine tuning. Then the printer setup has to have more
> consistency than the iteration feature delivers. I wonder whether that
> is possible with the desktop printers. Increasing the target steps in
> both linearising and profiling to 70 steps at most + an iteration of a
> 200-256 step tablet to one of them may be a solution. For the densito-
> spectrometer and the software it should be better/easier if that was
> done in the linearisation. The profile could then probably be based on
> far less than 70 readings.

Unfortunately this assumes that people are able to linearize.  This is not
possible if one wanted to use the Epson driver eg Adv B&W or black only.  My
suggestion would be to leave QTR as is and build the next stage - a program
to profile its results (or the results of any other workflow).

One question for Roy:  in the LINEARIZE function in QTR, is there a
prescribed number of/limit to the number of data points?

I agree with Roy that he/we (if we can help) need to iron out the
methodology first before it gets cut loose.  The white point thing is an
issue and I am surprised that correcting the wptp tag to the actual media
white point has not worked.  That, plus an accurate kTRC which shows the
input/output profile of the greyscale (all of the scale including the white
point) should have worked.  (There are no other required fields, other than
header info, in a greyscale profile.)  It's my understanding that this is
the information used for the white point adjustment that Roy mentioned.
[Furthermore, I think perceptual rendering and relcol with black point
compensation are the same thing for greyscale.  We could add a bkpt tag set
at the media/ink black point to check.]

Roy, when you corrected the wptp tag did you also change the kTRC to reflect
the white end of the scale (rather than running it to 100,100)?

The problem with this ICC profile stuff is that the parameters (ie profile
tags) are very well outlined in the ICC specification but just how they
interoperate is not.  When I began my conversations with Phil Green he was
wondering why we didn't just use a curve in PS and I had to go through the
whole argument that a curve could be used to preview the printer greyscale
and a curve used to correct it (the s curve) but that the preview curve
would then have to be deleted prior to printing and the "generic iteration"
s curve would be different for every printer/ink/paper/workflow.  Hence the
desire to be able to profile the printer and use CM.  But what you quickly
realise is that there is no right way or wrong way to do a lot of stuff -
perceptual rendering for example has no defined methodology; it is entirely
up to the profile creator.

Steve