QTR-Quadtone RIP

Oliver and Duane, thanks for your info. 

Oliver, there is quite a bit that you presented that may be a bit 
technical for me, but I'll re-read and try to understand. 

I'm going to still try using QTR to print in color, and here's what 
I'm thinking: 

For printing Magenta only: 
 * default ink limit: 85
 * black boost: blank

Magenta Ink
 * Density 100
 * Limit: blank 
Otherwise, no changes to gray or toner curves, and no linearization 
(And I might repeat this, only using Cyan). 

For printing with Magenta and Yellow (to get Red), I'd do same 
settings for Magenta and repeat these settings for Yellow. 

I'll print at 1440x1440 super to get the dot structure I need for my 
etching plates. 

I have tried to understand QTR but mostly I'm baffeled by it all, so 
I'm sort of winging it (trying things without knowing what I'm 
doing). 

Any simple advice is appreciated. 


--- In QuadtoneRIP@yahoogroups.com, "Olivier" <odesmais@...> wrote:
> Both.
> Printing in essence is a binary process : a drop or no drop (let's 
put aside dot size for simplicity). On the paper, a color drop alone 
will render that color. If you lay down 2 drops, both will have their 
corresponding primary color.  Now when many drops are laid down some 
will be covering or overlapping each other so an M dot will partly  
cover a Y drop and their will be 4 fractional area coverages: white, 
Y, M and M+Y (R). This process has been well defined by Neugebauer 
(for litterature reference) and a CMJN model delivers 16 different 
> fractional area coverages with their own spectral reflectance. 

Besides, light reflection is not just the light hits the surface then 
is either absorbed or reflected, a part is penetrating into the 
substrate because ink is translucid, scaterred and reflected back out 
of the paper at any probabilistic point (can be from where it entered 
or else), as such you have both a substractive and additive color 
model. 

The Neugebauer model doesn't not take that into account and is being 
modified by Yule Nielsen by an empirical factor (let's call it dot 
gain correction though it's not).

QTR can't do that because many factors are unknown. For instance, you 
can mesure the overall reflectance of a given sample but not the 
individual fractional area coverages to sum them up. However, you 
don't either really need it because QTR curve tool partitions inks 
based on relative density corrected of dot gain. Since many 
combinations of curves will output the targeted levels (BO would also 
for instance), all that is needed is to make the overall output 
linear. Now add one additional variable which is granularity (hope 
this is the right English word, correct me if wrong), and that 
becomes another game because there *is* then a single combination 
that delivers both best achievable linearity and smoothness...but be 
ready for frustration.

> Olivier