QTR-Quadtone RIP

Louis Dina wrote:
> 
> I found that using BO in my profile did give me the same Dmax as I 
> originally got in the MK step wedge when printing the original 
> inkseparation file.  In this test, I printed on Red River Aurora 
> Natural paper, and hit a Dmax of 1.65 on my 4000 at 85% ink.  I got 
> this on the inkseparation target and a BO profile using only the MK 
> with an 85% ink limit.  (This is using the MISPro color inkset - UC 
> equivalents).
> 
> I also tried the counterintuitive move in increasing the overlap of 
> the lighter inks (it was originally set to 0).  I tried an overlap of 
> 10 and 20.  They both slightly reduced the Dmax to about 1.63, but 
> that was less loss than I anticipated.  The neutral profile I built 
> had LK, LC and LM inks for neutrality and smoothness in the light 
> tones.
> 
> This leads me to conclude that the addition of light inks into the 
> shadows is, in fact, slightly reducing Dmax in most of my profiles.  
> I don't see a way of completely eliminating this using the normal 
> tools in QTR's Gray Ink tab.  You can minimize it by moving the 
> Shadow field in the Gray Curve Tab to a lower number (closer to 
> zero), which limits the use of light inks in the shadows.  To 
> completely eliminate light inks in the last step of the step wedge, 
> I'd probably have to create a plot list or import a curve from PS 
> (which may be my next experiment).  
> 

Louis

I just did a quick test to see exactly what the overlap figure does to 
the numbers. (You probably know that you can open the .quad files that 
are produced by the curve creation process.) With an overlap of zero the 
output for the LK curve at point 255 (ie 100% black) is 0 although at 
point 254 it does start to come in. As overlap is increased the amount 
of LK present at point 255 also increases as one would expect. In theory 
therefore 100% black with an overlap of zero should be giving you only 
the black ink. Changing the highlight & shadow settings did not alter this.

I don't therefore understand the Dmax results you are getting. As you 
suggested earlier using the point list curve input might be worth 
trying. You could take the visual representation of the curves to 
approximate your points but then just alter the LK slightly so it 
doesn't come in until say 90%.

regards
Howard