QTR-Quadtone RIP

Any recommendations on how to fix small bumps that persist after linearization? By `small bump' I mean a 2% or so deviation from the ideal linearization for any given point on the line. For example, I did a warm Eboni-4-Plus  curve for Alise Natural on my Epson 1400, and the curve is perfectly linear (i.e. the points deviate less than 1%) except at the 50% and 80% patches, which are 1.5% and 2.5% lighter than ideal, respectively.

I grant that these two small bumps might not be noticeable in prints, but I'd like to get a perfect curve if I can.

Thanks, 

Mark

Since nobody has jumped in on this, I'll give a quick description of what  
I have done. Mine is a strictly manual operation. Copy the data from the  
appropriate .quad file into Excel or OpenOffice Calc and separate the  
individual ink curves. You can create a composite curve by applying your  
relative ink density values to each ink curve and then combining the  
resulting values. Graph the ink curves and locate the areas where the  
"bumps" are located. Look for any suspicious inflections in the underlying  
ink curves at those points and manually change the values to straighten  
them out. Then copy the resulting data values back into the .quad file.  
Then do a new test print and check to see if the changes have helped.

Once you have manually edited the .quad data, you can no longer use the  
QTR program to make any changes or new linearizations.

I realize my quick description may not be adequate without a much more  
detailed explanation. If you need help, please contact me off list.

As a previous poster said:

"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"

I also have fussed over rings in the Northlight Images circular gradients  
pattern. For the most part, small "bumps" might not be visible in most  
images, but if you have large areas of a smooth gradient, such as a sky,  
they may show up.

Steve


      On Wed, 08 Feb 2012 06:51:49 -0800, mccarvill <mccarvill@...>  
wrote:

> Any recommendations on how to fix small bumps that persist after  
> linearization? By `small bump' I mean a 2% or so deviation from the  
> ideal linearization for any given point on the line. For example, I did  
> a warm Eboni-4-Plus  curve for Alise Natural on my Epson 1400, and the  
> curve is perfectly linear (i.e. the points deviate less than 1%) except  
> at the 50% and 80% patches, which are 1.5% and 2.5% lighter than ideal,  
> respectively.
>
> I grant that these two small bumps might not be noticeable in prints,  
> but I'd like to get a perfect curve if I can.
>
> Thanks,
>
> Mark
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>


-- 
Using Opera's revolutionary email client: http://www.opera.com/mail/

Many thanks for the reply, Steve.

<Copy the data from the appropriate .quad file into Excel>

I opened a .quad file in Excel and graphed a couple of the ink positions, but need more details on how to effectively work with this data using this technique. 

An easier (for me) alternative has been to create a Photoshop adjustment curve and lighten / darken the points that need it. This works, but I was hoping to do everything in QTR. But this seems impossible since I'll usually be blending curves, which necessitates some post-QTR tweaking. I've found that two very linear curves (i.e. my warm and cool curves) don't blend in a perfectly linear way.

< 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.>

I acknowledge this may be the case, but I know I'll be more content if I obsess a while longer on creating the most linear curves I can!

Mark 
 

--- In QuadtoneRIP@yahoogroups.com, "Steve and Ann Taylor" <taylorfamily3688@...> wrote:

>
> Since nobody has jumped in on this, I'll give a quick description of what  
> I have done. Mine is a strictly manual operation. Copy the data from the  
> appropriate .quad file into Excel or OpenOffice Calc and separate the  
> individual ink curves. You can create a composite curve by applying your  
> relative ink density values to each ink curve and then combining the  
> resulting values. Graph the ink curves and locate the areas where the  
> "bumps" are located. Look for any suspicious inflections in the underlying  
> ink curves at those points and manually change the values to straighten  
> them out. Then copy the resulting data values back into the .quad file.  
> Then do a new test print and check to see if the changes have helped.
> 
> Once you have manually edited the .quad data, you can no longer use the  
> QTR program to make any changes or new linearizations.
> 
> I realize my quick description may not be adequate without a much more  
> detailed explanation. If you need help, please contact me off list.
> 
> As a previous poster said:
> 
> "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"
> 
> I also have fussed over rings in the Northlight Images circular gradients  
> pattern. For the most part, small "bumps" might not be visible in most  
> images, but if you have large areas of a smooth gradient, such as a sky,  
> they may show up.
> 
> Steve
> 
> 
>       On Wed, 08 Feb 2012 06:51:49 -0800, mccarvill <mccarvill@...>  
> wrote:
> 
> > Any recommendations on how to fix small bumps that persist after  
> > linearization? By `small bump' I mean a 2% or so deviation from the  
> > ideal linearization for any given point on the line. For example, I did  
> > a warm Eboni-4-Plus  curve for Alise Natural on my Epson 1400, and the  
> > curve is perfectly linear (i.e. the points deviate less than 1%) except  
> > at the 50% and 80% patches, which are 1.5% and 2.5% lighter than ideal,  
> > respectively.
> >
> > I grant that these two small bumps might not be noticeable in prints,  
> > but I'd like to get a perfect curve if I can.
> >
> > Thanks,
> >
> > Mark
> >
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> 
> 
> -- 
> Using Opera's revolutionary email client: http://www.opera.com/mail/
>

Assuming that you use a spectrophotometer to measure the patches, bring your data (% black and L*a*b*) into Excel and plot each L, a, b, vs. % black.  Starting with the L vs. %K data plot, inspect for inconsistent points (anomolies)and delete them from the colum of L values.  Then add a 6th order polynomial trendline and check the box to show the trendline equation.  Use these coefficients to generate a "model" curve using the %K as "X" values.  Optionally, do the same for the "a" and "b" values.  Copy the "model" output values into the L*a*b values in a QTR-compatible text file, save it and drop this onto the "QTR-linearize" droplet.  Copy the linearized values into the curve description file and you should have (nearly) perfectly smooth curve(s).  The only problem I've seen with this method is that occasionally, if you have too high an ink density, the "model" curve may increase slightly at the highest %K values.  If this happens, just manually edit the last point or two to give slightly decresing L values.