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Problem with linearization

2011-09-18 by jeanyvesthuret

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

Re: Problem with linearization

2011-09-19 by jeanyvesthuret

Hi,

Obviously, there is a lot I don't understand with QTR. I tried to follow the protocol explained by Paul Roark in one of the .txt profiles for my printer. The first step is the determination of the dmax. Using the ColorMunki, I determined that the dmax occured at 60% for my printer, inks, and paper.
But where do I go from here as I couldn't find a folder called Tool, and an application called Curve Creation... I assume it is from the Windows version, or a previous version of QTR for MacOS. I tried to manually set the limit at 60 by changing the LIMIT_MK=70 to LIMIT_MK=60, but this results in a .quad profile that shows a total max of 51 when viewed in QTR-CurveView... On the other hand, the 3MK-Start profile has LIMIT_MK=70, but a total max of 60 when viewed in QTR-CurveView. This would mean that there is a 0.85 factor somewhere, but I can't find it in the description .txt file.
I am lost. Could someone point me to a tutorial for curve design in the current QTR in MacOS ?

Thanks in advance

Jean-Yves

--- In QuadtoneRIP@yahoogroups.com, "jeanyvesthuret" <jeanyvesthuret@...> wrote:

Show quoted textHide quoted text

>
> 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
>

Re: Problem with linearization

2012-01-13 by amothol

Hi,
i am also going through the learning curve. Today i went trough the tutorial in the file section of this group: Building QTR Profiles with Mac's_v4.pdf. I can recommend this tutorial.
Matthias

--- In QuadtoneRIP@yahoogroups.com, "jeanyvesthuret" <jeanyvesthuret@...> wrote:

Show quoted textHide quoted text

>
> Hi,
> 
> Obviously, there is a lot I don't understand with QTR. I tried to follow the protocol explained by Paul Roark in one of the .txt profiles for my printer. The first step is the determination of the dmax. Using the ColorMunki, I determined that the dmax occured at 60% for my printer, inks, and paper.
> But where do I go from here as I couldn't find a folder called Tool, and an application called Curve Creation... I assume it is from the Windows version, or a previous version of QTR for MacOS. I tried to manually set the limit at 60 by changing the LIMIT_MK=70 to LIMIT_MK=60, but this results in a .quad profile that shows a total max of 51 when viewed in QTR-CurveView... On the other hand, the 3MK-Start profile has LIMIT_MK=70, but a total max of 60 when viewed in QTR-CurveView. This would mean that there is a 0.85 factor somewhere, but I can't find it in the description .txt file.
> I am lost. Could someone point me to a tutorial for curve design in the current QTR in MacOS ?
> 
> Thanks in advance
> 
> Jean-Yves
> 
> --- 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
> >
>

Re: Problem with linearization

2012-01-15 by David

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:

Show quoted textHide quoted text

>
> 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
>

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