QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@c...> wrote:
> Roy Harrington wrote:
> 
> >--- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@c...> wrote:
> >  
> >
> >>There was a problem reported in the lists with the 51 linearisation some 
> >>time ago. Steve Kale ?
> >>Is that solved ?
> >>Will QTR work with a custom range of 41 steps if the 51 range is too 
> >>subtle for measurements-computing ?
> >>So far I have not seen linearisation ranges that go beyond 40 patches.
> >>
> >>Ernst
> >>    
> >>
> >
> >The Linearization does work with 51 steps but since the step values are
> >closer its a little more sensitive to lack of separation betweem the steps.
> >  
> >
> That's what I expected to be the cause.
> 
> 
> >For the most part I think 21 is plenty.  Compared to color charts that are 
> >commonly used this is way more data points per dimension -- 1000 patches
> >for color in 3 dimension is only 10 point per dimension.
> >
> >  
> >
> 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.
> 
> 21 should be good for B&W systems K2-K3-(K4). But for a K7 set it means 
> 3 measure points per ink channel (head) which is too low in quantity. 
> 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. 51 for K7 is in 
> that category. A linearisation target that falls in between the two 
> would be nice for K4-K6 inksets. lt has more measurements per head than 
> the 21 and more separation between the steps than the 51.
> 
> While it wasn't an easy job to change the Wasatch SoftRip into quad 
> printing it had the linearisation at inkchannel level. The CcMm 
> inchannels had a K4 setup and together 28 steps for measurement. The 
> toners each 14. On top of that the separation curves were build. I 
> checked the linearisation of the total then with 21 or 44 steps to get 
> the curves right and added a curve (very subjective) to get the 
> perceptual linearisation. This is all much easier in QTR. However I 
> think that the relation between the step number and the total of printer 
> heads measured shouldn't be forgotten.
> 
> 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.
> 
> Ernst

Interesting comments.  I hadn't thought to compare the number of steps
with the number of ink partitions.  It probably depends somewhat on the
method used to partition the inks.  QTR uses a special algorithm that takes
into account the relative densities of the inks so the transitions don't have
flat spots and all 256 values per ink are calculated rather than just smoothly
connected.  In any case I've made some K7 profiles and I haven't noticed any 
issues with it.

Another factor that I'm beginning to think is also more important is the
variable dotsize of the printers.  My main printer has been the 7500 which has
only one drop size and linearity has always been very smooth.  But my smaller
printers are all variable dot and I think that may be a large factor in their more
bumpy linearity per ink.  Once you add a bunch of inks the bumps usually even out.

Roy