QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@c...> ...
snip...
> The targets you mention are the ICC profiling targets that usually
build 
> on linearised inkchannels. Linearisation targets exist in many shapes 
> CMYK-CcMmYK-Ncolor and they have ranges of 11 to 41 patches per 
> inkchannel. the lowest number can be used for printsystems that
actually 
> address the heads separately but on a CMYK driver that is linearised as 
> CMYK but drives a CcMmYK printer it is better to use the 21 patches so 
> there are 10 steps measured per head. With the 4800 that has 3Ks you 
> could go up to 31 steps and that has been used for Colorspan models
that 
> have 3 ink dilutions of CMYK each = 12 heads.

My impression of the process is a bit different, correct me if I'm
worng. Individual ink components of a color, C and c for example, or
the 3Ks you mention, are generally not addressed individually in the
linearization process.  Some control is usually given with respect to
how the transitions will happen, but then the color (all inclusive
"C", or"K") is linearized as one. How exactly the total patch  count
may divide up between those indivicual components may not be very tidy.
I'm sure this varies from RIP to RIP. I recall Roy asking if we
thought there would be an advantage to individul ink linearization,
and wonder the same thing myself.

> 21 should be good for B&W systems K2-K3-(K4).

I have on occassion seen an advantage to doing many more here with 4,
and wound up at 80. I've seen a higher count like this fix problems
between say 95% and 100%, more than once.

> But for a K7 set it means 
> 3 measure points per ink channel (head) which is too low in quantity.

The above may apply here again. It seems, under the curcumstances, we
are somewhat at the mercy of the partitioning scheme. If it's  very
well behaved and designed for the ink set and media, a good overall
linearization (with an adequate patch count as you are discussing)
should work well.
In fact this seems to be what we are all doing for now anyway. The
downside is that a less then stellar partition scheme can be bad
enough that overall linearization will not fix it.
With what most people are using, that doesn't seem to happen much.

> The CMYK linearisation of the Wasatch SoftRip has 14 patches per color, 
> on the Cc and Mm inkchannels of the 9000 it means 7 patches per C,c,M,m 
> head and I think that's about the lowest you can go.

So it does allow you to linearize each color component individually?
Studioprint does not, though it allows one to enter any per color
patch count number they want, I'm sure there is an upper limit, I
think 100?
Set's with toners present a challenge as well, it's not a common color
model SP is preset to work with. Sounds like your RIP has some options
there you  have bent to your will <G>.
 
...snip...

> The ICC profiling done with the 21 step target on top of the 
> linearisation done with the same 21 step target may work as an
iterative 
> measurement as well and so average the result a bit (it produces
another 
> curve of course) but whether that is sufficient for B&W sets above K4 
> isn't clear. I think there's improvement possible.

no doubt. But the partitioning step needs to be considered as a major
part of the overall performance picture. How many patches and how much
work needs to be done at the end can have a lot to do with how well
behaved the ramp is to begin with.
That few have trouble with QTR speaks well of Roy's existing
partitioning scheme. Setting it up to pull 7 inks in and out without
major problems must have been fun, or not!
Tyler