QTR-Quadtone RIP

I have also found lots of rings with the Northlight Images circular gradients, using my profiles for the UT14 inkset.  I think that the circular gradients are especially sensitive to small bumps in the curve, but don't reflect the overall linearity much. 

I spent some time trying to tweak the curves to make the rings go away.  Eventually, I stopped printing circular gradients and have been much more content since then.  I don't think that I have seen anything in a real print that reflects this artifact.

David



--- In QuadtoneRIP@yahoogroups.com, "jeanyvesthuret" <jeanyvesthuret@...> wrote:
>
> Dear All,
> 
> I have started using QTR with a R800 and the 3MK inkset from MIS. I am using an Epson Archival Paper had tried to linearize the profile for this printer/ink combination, using a ColorMunki spectrometer. I am using the 21-step wedge on Keith Cooper test image, found at Northlight Images (www.northlight-images.co.uk/digital_black_white.html). Printing was almost linear from the start, with the 3MK-Start profile, except that the 95% black had the same L value as the 100% black. After linearization, this was solved as expected (perfectly linear L-value vs %black after rescanning). In the test image, I had more details in the shadows, as expected. So far, so good. The only problem is that the circular gradient from 0% to 100% black, which was almost perfect before linearization, is now all messed up, with lots of rings, which would indicated non-linearity. There must be something that I don't understand, or a weird artefact with QTR and circular gradients ?
> Any help will be highly appreciated !
> 
> Jean-Yves
>