QTR-Quadtone RIP

With the R1800 3MK set up (3 Eboni and 5 cleaning cartridges) run by a Mac I was having 
trouble with banding in large areas of even midtones. This was prominent all across the print 
in images with a lot of sky, not just the edges, using Premier Art 270 and 325g papers. I 
recalled a post (but can't find it now...) by Paul mentioning he had tried 4MK and gotten 
marginally smoother prints, thought this might help the problem. I added an Eboni cartridge 
to the C position. Having no Idea what I was doing I tried converting Paul's profile for the 
Premier 270 to 4MK: In addition to the obvious edits I cut the LIMIT from 70 to 52.5 for the 4 
inks (sum still = 210 if that is important). I duplicated the CURVE for the GL and used it for 
the C position as well, this was a random choice. I am curious why the original 3 curves differ 
slightly for the MK, PK and GL positions and wonder if a new, different curve is needed for the 
added C position?
Didn't re-linearize.
The results appear very good, the banding is effectively gone, and to my eye the prints look 
otherwise like the 3MK versions. 
Am I missing anything, or is it a safe bet to use this approach in general for getting to 4MK? 
It certainly seems to help my print quality.
Thank you,
Harlan

Hi Harlan,

>With the R1800 3MK set up (3 Eboni and 5 cleaning cartridges) ...
> I was having trouble with banding in large areas of even midtones.

Be sure you're running at 2880.  I get such banding at 1440, but it clears
at 2880.  However, I suspect there are individual printer differences.

>I recalled a post ... Paul mentioning he had tried 4MK and 
>gotten marginally smoother prints, thought this might help the problem.

Yes.  It was very close on my printer, so the ability to run color was the
deciding factor.  (I, however, also run cleaning fluid in the other jets.)

> I added an Eboni cartridge to the C position...
> tried converting Paul's profile for the Premier 270 to 4MK: 
> cut the LIMIT from 70 to 52.5 for the 4 inks (sum still = 210 
>if that is important).

You could run a dmax test similar to the one in the QTR folder, but with all
4 inks firing.

> I duplicated the CURVE for the GL and used it for 
> the C position as well, this was a random choice. 

>I am curious why the original 3 curves differ 
>slightly for the MK, PK and GL positions and wonder if a new, 
> different curve is needed for the added C position?

I found when the curves were at the same place and with the same slope,
there was a tendency to show little vertical lines.  So, the idea is to have
the jets firing slightly different patterns.

>Didn't re-linearize.
>The results appear very good, the banding is effectively gone, 
>and to my eye the prints look otherwise like the 3MK versions. 

It looks like you've done what needed to be done.  You might want to run a
dmax test and re-linearize.  You can do these things even with a flatbed
scanner.  If there is any evidence of the GL & C inks starting, you could
have them start at different points.  If you see any evidence of those
little vertical lines, just vary the curves a bit.

Good luck with the system.

Paul
www.PaulRoark.com