QTR-Quadtone RIP

Not a lot of time, but here is a quick response.

What you are setting in QTR is at a more "detailed" level than an ICC 
profile. You atre really setting up a generic "driver" the program 
taht puts the ink on the paper. 

Imagine you work for Epson. They ask you to write a driver to make 
prints on their next printer. Grey inks only - no color - to make it 
a little easier for your first driver. ;>)

Your first question: How many inks? 

That corresponds to the number of inks that you set in QTR as "Grey 
ink." You might tell it, for example, that the Black (K), Light Black 
(LK), and Cyan (C) positions have an ink cartridge in them.  The M, 
LC, LM, and Y positions have no ink (or a color ink) so you leave 
those unused.

The next question: "Which ink is darkest?"  "By how much?"

The "L" value ranges from 0 to 100. 0 is the darkest, 100 is the 
lightest.

You use the "Density" value to enter the "L" value that you read from 
a patch of ink to tell QTR how dark an ink is. First you set the 
value of the darkest ink, K.  

The values you enter for the other inks are relative, in terms of the 
darkest ink - usually K.  They tell QTR how much "lighter" those inks 
are than K.

So you enter the denisty of "LK" as a 40, that tells QTR that the 
darkest that LK gets in the printout is the same as K at the 40 
level, a litte less than halfway to black on K's "white" to "black" 
scale. 

And then you enter a 13 for C. That says that C is lighter than K or 
LK, that the blackest it gets in the test printout is equal to K at 
the 13 level.  

So C is more useful for highlights than shadows. LK will be useful 
for midtones. And when you need a dark black, K will be used for the 
shadows.  

Next question: "How do I know when to stop adding more ink?"

The answer: at the point of diminishing returns for any given 
dilution.  That is, as you put more ink on the paper, the patch 
usually becomes darker - which is good. But there comes a point where 
you keep adding ink, anbd the patch becomes just barely darker, or 
actually becomes a little lighter. That is the "Limit", the point at 
which you stop adding ink (and probably switch to your next darker 
ink.)  If you didn't have a limit, you could keep addinmg ink - 
trying to get a draker black - until you had puddles on the paper 
taht smeared and created a holy mess.

OK, you enter all of that. QTR makes a print, but there are jumps and 
gaps in the values it outputs, especially when it switches from one 
ink to the next. So you "linerize" it - make the output appear 
smooth, or continous, to the eye, so that there aren't weird things 
going on when it switches from the C to LK ink - like suddenly 
getting darker by 15 units, instead of 1 or 2 "L" values.

I hope that helps.   More questions?

Best,
michael