QTR-Quadtone RIP

Louis Dina wrote:
> That's my understanding too. Linearization is a one shot deal.  If 
> you try linearizing again over a previous linearization, your new lin 
> data will overwrite the old lin data, and you will not have a good 
> linearized profile.  I also agree that QTR does an excellent job of 
> linearization and separation of tones.  

Iterative measurements can be an interesting option if (and 
it is a big 3 fold IF) the measuring instrument, the 
measurements and the printed targets are much more 
consistent than the linearisation fault you want to correct. 
There's more to gain in my opinion with multiple readings of 
more random linearisation targets that are printed at two 
angles to the print direction and building the linearisation 
on the average of the measurements.

For color profile creation the iterative build-up has been 
discussed on the colorsync list maybe two years ago and 
while there's color profiling software that allows iterative 
measurements the parties were divided on the pros of it. 
Considering the more complex shape of a profile and its 
function to represent the printer's color space the 
iterative function in the software could improve the shape. 
The same IFs apply there too. But if that can be achieved 
and when used on good regular calibration routines of 
printer + paper batches to keep the underlying base 
consistent it is in theory not a bad concept. The 
calibration done as suggested with multiple readings etc.

I use two terms: calibration and linearisation.
The first doesn't have to be a linearisation but sets the 
printer to fixed output numbers based on target readings, 
including the Dmax. So as I understand it, if that printer 
delivers more Dmax than the factory prescribes the inklimit 
at 100% will also be set lower for that channel. The 
uncalibrated channel could give a higher inkload (which 
isn't always a higher Dmax) than the calibrated channel.
Linearisation is done between paper white and the Dmax 
measured and as the first and last could vary the steps in 
between could vary. A profile made earlier on the first 
linearisation may not represent the printer after a new 
linearisation. The linearised and unlinearised channel 
should have the same Dmax.
What manufacturers did implant in the functions and how they 
describe them is not always clear, hybrids of the two are 
possible too and do not have to be bad either.

For sophisticated color profile creation with an iterative 
build up you better start with a calibration to squeeze out 
the last inconsistency in the base before the sculpturing 
and polishing happens on top. I doubt that this all is 
needed for B&W printing with QTR.

Again, there's more to gain in my opinion with multiple 
readings of more random linearisation targets that are 
printed at two angles to the print direction and building 
the linearisation on the average of the measurements. Same 
for the QTR profile.


-- 
Met vriendelijke groeten, Ernst


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