QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, "brigsby707" <brigsby707@c...> 
wrote:
> Hi Howard,
> 
> I might just be repeating what others have written, but I'll send 
this anyway in case it 
> might help.
> 
> I'm pretty new to this whole process and ran into the same 
situation.  So, in regard to 
> being new at it, if anyone sees anything that I suggest, that might 
be a little off or could 
> be clarified further, don't hesitate to do so.
> 
> What I've found is that if your assessing the ink limits by eye, 
you're going to want to look 
> for an area where the paper is covered and subsequent patches level 
off as far as getting 
> darker.  Granted that still leaves room for interpretation, but it 
might get you a little 
> closer.
> 
> Now, if you have access to a densitometer, a spectrophotometer or 
at least a reasonably 
> decent scanner with an image editing program capable of working in 
a Lab color space, or 
> a scanner capable of reading L values (sometimes there is 
a "densitomer" feature capable 
> of doing this, that can be used in the scanning process) you can 
approach it a little more 
> "scientifically."  Basically what you would want to do is measure 
either densities or L values 
> of the patches, then determine numerically, where the values level 
off.  I personally have 
> been using my Epson 4990 scanner and Photoshop to do this.  I 
basically just scan the 
> image into Photoshop, convert the image to the Lab color space, 
then do the reading with 
> the color sampling tool set to average the value of a 5x5 pixel 
area.
> 
> As for setting different limits, I've only been able to do so, when 
creating the final profile. 
> So in order to determine the relative values, ie: dark grey = 50% 
black, I've just taken 
> whatever patch I determined to be the ink limit for the different 
gray values and compared 
> that to a print out of a temporary, black only profile (created by 
indicating only one "gray" 
> ink, and setting the rest as unused), since I haven't been able to 
do the separation page 
> with a new general ink limit (actually if anyone could fill me in 
on that one, it would be 
> helpful).  However, I should note that, following this procedure 
I've had great results, in 
> that you can then determine whatever limits you want for each ink 
and maximize your ink 
> usage.  For instance, I'm using an Epson 1280 with Piezotone inks, 
and have regularly 
> found that the black ink, maxes out long before the other inks, so 
I create the black only 
> profile with the black set to say 55%, print it, and then compare 
that (by scanning into 
> photoshop) to the original ink separation printout to find the 
relative values with the inks 
> that often max out around 85-90%..
> 
> Anyway, hope all that helps.
> 
> Regards,
> 
> Eric

Seems we have the same settings : 1280 + Piezo. Besides, Eric sounds 
French : are you French. I am.

I've started experimenting QTR about 2 weeks ago (shame on me I did 
not yet pay my fee, but I intend to once I end the experimentation 
and start producing prints) with PiezoBW ICC inks, HWmatte and EEM 
(I'll go for Velvet once I feel I understand it all), 1280 and an X-
rite spectro dropping mesures in Colorshop X.

I have been so far relatively successful in creating a fairly 
reasonably acceptable curve. I've tested Epson Heavyweight matte : 
very easy to get a curve and EEM : far more complicated, but I admit 
even for color profiling this paper is a nightmare. I have not yet 
gone in to the blackboost (so I just apply the 10-15% more than ink 
limit rule), the highlight-shadow fine tuning (just use 8 and 4 as 
per Roy's recommendations) and I'm still struggling a bit 
undertsanding the latest ICC features (no problem to create the 
profile, just need to really understand the way it has been be 
applied). 

What I discovered on both papers is that the Black ink limit has to 
be fairly low if you want to get a smooth grayscale : the additional 
ink will only bring troubles to linearise as the black end of the 
separationink mesures will get very messy. I ended with a 1.62 
density which is enough for me and a great smoothness which was my 
initial goal. On Piezo NeutralWarm and HW matte general ink limit was 
measured at 55, with EEM at 70 (which I assume is still too high), 
then C is 35 and M 11, Y 5. Based on these values I have a fairly 
nice grayscale though in the 80-85% of the setpwedge I feel there is 
a small bump, I need to re-do the curve on EEM with general ink limit 
at 65 to see if the smoothness improves (the density varies all the 
time on this paper even though you allow long drying time : it's a 
real annoyance).

The only issue I got so far is to have the 6 heads firing on a single 
print : at the moment I have 1 curve KCMY and 1 KCLCLM. I have not 
been successful using the 2 same inks in 2 different positions for 
the same print and have an acceptable curve ; there is banding where 
I suspect the 2 same inks get into action (so 2 bands on the 
stepwedge). I've read you can either set M at the mesured density 
ratio and limit at 50 then set LC density at "copy from" M or simply 
have density ratio M at 11 and LC at 10 or 12 for instance : I have 
not tried yet (very time consuming and costful at the end of the day).

I'd be happy exchanging experiences if you wish so.

Olivier