QTR-Quadtone RIP

Hi Ernst.  

--- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@...> wrote:

> Where do you limit black ink itself, right at the point 
> where no density increase happens or do you go a bit higher 
> where the extra ink shouldn't add more density in theory but 
> isn't taking density away either ? I have done the last in 
> the past with the idea that some reduction by the 
> linearisation curve just below 100% will solve a flat part 
> there but a stricter ink limit may loose density in the two 
> steps of linearising and profiling and/or fluctuations of 
> printer and paper coating. In short a slight bleed to be 
> preferred above any white appearing.

When I was using the typcal QTR controls, I found I got better 
profiles using a slightly lower default ink limit.  I would typically 
select an ink limit at the "shoulder" of the black black ink (for 
example, if Dmax was 1.68 at 75% ink, I might select 55 or 60% where 
the Dmax was around 1.6 or so and the curve was just 'beginning' to 
steepen).  This resulted in a lower total ink and better separation 
in the shadows.  I often found that setting the ink limit exactly at 
the Dmax caused the shadow steps to bunch up.  To get back the better 
Dmax, I set the black boost to 75%, corresponding to the best Dmax in 
my calibration print.  I have never gone to a higher ink load for the 
black, since my intial ramp in the calibration print always showed 
that the Dmax either stayed the same or dropped slightly.  

> On the darkest grey ink running close to the 100% and 
> reducing density I think it depends much on how dark that 
> grey ink is and how consistent the printer's dot pattern. I 
> had my doubts about the HP Z3100 quad use for  some matte 
> papers:  MK,PK,Medium Grey and Light Grey where the PK can 
> not bridge much of the tonal range so why use it.  But 
> before that I used the same configuration in my 9000 MIS 
> quad to fill in (to a degree) irregularities of the black 
> dot pattern. The same concept that is used in multihead BO 
> printing now en vogue. I have no idea how the HP Z3100 B&W 
> mode adds the PK in the partitioning but I think it is more 
> to deepen the black than for the shadow range. The HP B9180 
> doesn't have that quad partitioning but has superb 4800 
> lines stepping resolution hardware and 1000 nozzles per head 
> so also for the black. Based on that is a superb screening 
> resolution and patterns with 16 bit screening masks. No need 
> for PK to close the ranks. When Roy made QTR the printers he 
> had to work with then could use a bit of overflow from the 
> dark grey ink instead of relying on the black only. It may 
> not have been intentional but I guess he did work with trial 
> and error. No problem, no solution needed. Now with better 
> resolution and consistency this may be no longer the case.

Very interesting comments on the HP printers and the older printers.  
I'm using an Epson 4000 and a 2200.  What I have been doing recently 
is creating my own curves using the Plot Lists in QTR.  This allows 
me to totally control the shape of the curves, and also where each 
ink starts and ends.  I am using MISPro color inks (UltraChrome 
equivalents), so in addition to the Eboni black, I typically use LK, 
LC and LM (I only use Y with my sepia profiles).  These inks are 
fairly light, and I believe they do reduce Dmax slightly due to 
overlap, at least in my testing and using my methods.  Using plot 
lists, I have stopped all light inks past about 95%, so only the 
Eboni is used for solid black.  I am using 2880 dpi, unidirectional 
printing and the ordered dither pattern, so I get good coverage with 
Eboni only, and I don't see any white at all when viewing with a 
loupe.  

Another advantage of using plot lists is that my curves are almost 
perfectly linear before performing final linearization.  That should 
provide better profiles overall, though I am not sure if it is 
noticeable or not.  Building the initial set of curves with plot 
lists is time consuming.....but....over the next weeek, I am planning 
to repurpose my initial profiles and see how they migrate to 
different papers, and even different printers.  I am hoping I can 
simply determine the correct ink limit for the new paper, print a 
test strip, and relinearize.  If that is successful, it will be very 
fast and easy to build new profiles, and hopefully, they will be more 
consistent from one paper to another.  It should also allow me to get 
the best Dmax that paper is capable of, without any loss due to light 
ink overlap.  I'll report back.

Regards, 

Lou