QTR-Quadtone RIP

Howard Shaw wrote:
> Ernst Dinkla wrote:
> 
>> 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.
>>
> 
> Ernst
> 
> Could you summarise what the advantages of random targets are over 
> ordered ones? They are rather inconvenient for those of us with more 
> primitive devices.
> 
> Also could you please explain what you mean by printing the target at 
> two angles. Do you mean in portrait & in landscape modes? If so why 
> would that be necessary?
> 
> thanks & regards
> Howard

In row reading spectrometers and densitometers can be 
influenced by a light patch before reading a dark patch, the 
more contrast the more likely to happen, sensor memory. So 
reading greyscale step wedges going upwards in density or 
downwards should give different readings as well. On the 
Epson 9000 quad I also observed that I got a more equal 
output if the head had been busy before printing the target 
than if it just had to start with the target itself. Next to 
that comes banding (can be almost invisible) in the inkjet 
printed target and a dominant grain direction in the paper. 
The print will lay down its ink different and/or the 
spectrometer gets another reflection from the surface. For 
example (textured) art papers made on the foudrinier, or 
worse, canvas. There is also the inconsistency of the manual 
measurements in row reading. So printing multiple random 
targets at different angles to the paper and print direction 
isn't a bad idea. One could arrange them all at 45 degrees 
but on the 9000 I had two in one direction and one in the 
other covering the width of a roll together. Faster in 
printing, the roll could stay on the printer, less paper 
waste and more related to the printing done in practice, 
drying between passes etc. I have an old helmet type hair 
dryer on a box to speed up drying of the targets.

Whether it is all necessary depends on how good the 
measuring method is, the quality of equipment and how anal 
one is :-)

The HP Z3100 that I have now prints the calibration target 
(16 patches per channel, 11-12 channels) in the paper 
transport direction. Steps are not random but go up and down 
in that direction. Quite big patches. After drying time it 
will measure per patch in the head direction, measurements 
on the dark patches are done longer than the light ones. 
With profiles one can either let the target dry on the 
printer or take it out and do the measurements later on. The 
Z3100 ink settles faster so it works well on the printer.

-- 
Met vriendelijke groeten, Ernst


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