QTR-Quadtone RIP

Thanks, Tom. I did respond to Terence, but included more details in my
response to Jeff. I do appreciate everyone taking the time to help
out. I encountered a number of error messages when trying to gen
curves, load acv's, load profiles for editing, etc. which is
stretching my learning curve :) If someone is interested I could send
a summary of these offline. I haven't been able to find an error log 
for QTR -- does it maintain one? Would be helpful, especially as one
can't cut/paste from the error dialogs generated by the GUI.


--- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@...> wrote:
>
> --- In QuadtoneRIP@yahoogroups.com, "Philip Schwartz" <pschwart@>
> wrote:
> >
> > Thanks for the clarity of your explanation -- I now see the workflow
> > in my original post was way too sketchy :) I am actually following
> > exactly the process you describe. 
> 
>  Well, If you had responded to Terrence Lowe's post I wouldn't have
> written my detailed description.
> 
> I am obviously not using the
> > controls on the gray curve tab effectively. I'm sure the problem is
> > that the corrections I am making are not based on any understanding of
> > how the Highlight and Shadow parameters work on the Gray Curve tab.
> 
> Other than larger values give lighter tones, there is not much to
> understand. The rest is empirical.
> 
>  I
> > am clear on gamma, but I have been holding this param constant. I am
> > also using an Excel spreadsheet that plots the curve against the ideal
> > for a specific dMax. I think I just need to dive back in and get a
> > better feel for the QTR controls. I am also still not clear on exactly
> > how to partition inks and set limits, and if these decisions are
> > flawed, linearization is moot, but this is another topic. Any hints
> > here would be much appreciated.
> 
> Yes. This is another area where some experience helps. I think that
> setting ink limits can be the most common source of problems. Too much
> ink can cause the problems you are having. The partition values
> (relative densities) are less critical.
> 
> Creating your own curve for a paper/ink combination for which a curve
> is included in QTR, can be useful in understanding the methodology for
> curve creation.
> 
> Tom Moore
> 
> > 
> > --- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@> wrote:
> > >
> > > Phil
> > > 
> > > Looking over your posts on this topic it's not clear to me what
> you are
> > > changing on each iteration. I don't know of any mechanism in QTR
> for one
> > > linearization to refine the results of a previous linearization.
> > Iteration
> > > is useful, but as Terrence Lowe points out it should occur before
> > > linearization. To elaborate somewhat on Terence's suggestion, here's
> > what I
> > > do:
> > > 
> > > After the curve is setup on the Ink Setup tab and I am happy with
> > the limits
> > > etc on that tab, I print a step wedge, measure the values and plot
> > them in
> > > Excel. I compare this non linearized curve with the so called ideal
> > curve
> > > for the dmax I am achieving with the ink/paper I'm using. If there
> is a
> > > "big" discrepancy between the measure curve and ideal, I'll
adjust the
> > > Highlight, Shadow and Gamma parameters on the Gray Curve tab and
print
> > > another step wedge, measure and plot it. You may also have to
> adjust the
> > > same parameters on the Toner tabs if appropriate.
> > > 
> > > I don't have any suggestion as to how to judge "big". All I can
> > suggest is
> > > that if you're not happy with the results of linearizing your
> curve, you
> > > could try making your "big" smaller. Also, the Gray Curve
> parameters are
> > > sometimes useful in eliminating flat spots or small reversals that
> make
> > > linearization impossible.
> > > 
> > > I may adjust these parameters, print, measure and plot the results
> > several
> > > times before I feel the curve is close enough to get QTR to
> linearize it
> > > satisfactorily. After doing several curves the number of iterations
> > required
> > > drops off. Of course once you've done one curve for an ink/paper
> > combo you
> > > can usually use the same values for other curves for that paper - at
> > least
> > > as a starting point.
> > > 
> > > As an indication of how much adjustment can be required, the
> default and
> > > final values for these parameters for a curve I created for Premier
> > Fine Art
> > > are:
> > > Parameter       Default         Final		
> > > ---------       -------         -----
> > > Highlight         10              6
> > > Shadow            10              4
> > > Gamma              1             1.6
> > > 
> > > The Gamma adjusts the mid-tones and the other parameters adjust the
> > obvious
> > > parts of the curve. In general, "L"arger values "L"ighten the
> curve. As
> > > noted in the User Guide, the Gamma adjustments are dramatic and
> > should be
> > > small compared to the other 2 parameters. Once you reach acceptable
> > values
> > > for these parameters, you can use the measured values from the last
> > > iteration as the linearization values to create your final curve.
> If you
> > > need to adjust these parameters again, you must clear the
> linearization
> > > array and print and measure a step wedge so you can enter the new
> > > linearization values (and regenerate a new curve).
> > > 
> > > I recall that adjusting these parameters was suggested in a post
> by Roy
> > > because the linearization algorithm is not able to do an effective
> > job on
> > > curves that require a large adjustment. I don't recall him stating
> > how close
> > > you need to be to get a good linearization.
> > > 
> > > I created the curveval2.xls spreadsheet (available in the files
> > section) as
> > > a tool to aid in visualizing the curve. I use Xkey, a key-stroke
> grabber
> > > from X-Rite, to place the values from my 810 directly into the
> > spreadsheet.
> > > I find I can make a quite good (in my humble opinion) curve using
> the 21
> > > step wedge. The 51 step wedge is more work and, because of the
> > smaller step
> > > is more prone to reversals.
> > > 
> > > Hope this helps. Good luck.
> > > 
> > > Tom Moore
> > > 
> > > > -----Original Message-----
> > > > From: QuadtoneRIP@yahoogroups.com
> > [mailto:QuadtoneRIP@yahoogroups.com] On
> > > > Behalf Of Philip Schwartz
> > > > Sent: Wednesday, December 20, 2006 7:19 PM
> > > > To: QuadtoneRIP@yahoogroups.com
> > > > Subject: [QuadtoneRIP] Re:can't properly linearize ink profile
> in QTR
> > > > 2.4.3.10
> > > > 
> > > > Hi Jeff. I am familiar with Keith's image, but I didn't
actually try
> > > > it. My reasoning: I need to create curves that will produce
> > > > (reasonably) identical prints on different papers. If I can't
> reliably
> > > > linearize my profiles this will be an exercise in futility. I
> may get
> > > > good prints, but none will match. I did also try the 51-step
wedge,
> > > > but I kept getting QTR errors complaining that the linearization
> array
> > > > sequence was invalid because it was not constantly increasing so
> curve
> > > > generation failed. To be honest, I got this message most of
the time
> > > > using 21 values, but did manage to generate a couple of curves. It
> > > > seems like QTR doesn't like multiple steps with the same value, or
> > > > steps that are too close together, or, horrors, a value that
> actually
> > > > decreases. All of these things can happen in my world, and I don't
> > > > know how to fool QTR without invalidating my measurement.
> > > > I also tried to load a Photoshop CS acv I use all the time, but
> got a
> > > > QTR error about invalid values. Sorry, I'm not in front of that
> > > > computer at the moment but I have captured all these errors on
> my home
> > > >  PC.
> > > > --- In QuadtoneRIP@yahoogroups.com, "Jeff Randall" <jrandall@>
> wrote:
> > > > >
> > > > > Phil: Have you printed Keith Coopers test image
> > > > > <http://www.northlight-
> > > > > images.co.uk/article_pages/black_and_white_test.html>
> > > > > and looked at the circular gradient and printed the
> offsetgrad8.jpg
> > > > > file located in this group's Files section to see if you can
> > > > > actually see the non-linearities you are measuring?
> > > > >
> > > > > Another thing to try is a 51 step calibration approach using
> the 51-
> > > > > step file in the OneEye folder of the QTRip folder.  I had
> problems
> > > > > getting a linear profile using the 21-step approach, but the
> 51-step
> > > > > approach worked very well for me.  YMMV.
> > > > >
> > > > > BTW, I stretched the 51step image to print landscape -- bigger
> > > > > patches for my clumsy hands.
> > > > >
> > > > >
> > > > > --- In QuadtoneRIP@yahoogroups.com, "Philip Schwartz"
<pschwart@>
> > > > > wrote:
> > > > > >
> > > > > > Thanks Terence. I am a new to QTR but have lots of experience
> > > > > printing
> > > > > > fine art B&W. QTR has lots of controls, but they are not well
> > > > > > documented so results are often not predictable, making the
> > > > > profiling
> > > > > > process incredibly tedious. I am spending far too much time
> > > > > profiling,
> > > > > > and not enough time creating and printing images :( Hoping
this
> > > > > will
> > > > > > change ...
> > > > > >
> > > > > > --- In QuadtoneRIP@yahoogroups.com, Terence Lowe <televe@>
> wrote:
> > > > > > >
> > > > > > > I, too struggled with the QTR linearization process.  My
> > approach
> > > > > > was to
> > > > > > > try to get the best density measurements by modifying
the ink
> > > > > setup and
> > > > > > > grey curve tabs, but with the linearization array clear.
 This
> > > > > took
> > > > > > many
> > > > > > > iterations.  Eventually, when I thought that the measured
> > > > > density curve
> > > > > > > was close to the ideal density curve (I plotted both in
Excel
> > > > > for
> > > > > > > comparison purposes), I linearized, printed the step tablet
> > > > > again and
> > > > > > > checked the new, linearized density measurements to
> confirm (or
> > > > > > > otherwise) that my final curve was good enough.
> > > > > > >
> > > > > > > I made the assumption that it was incorrect to
> re-linearize the
> > > > > > > linearized curve during the many iterations and so only
> > > > > linearized once
> > > > > > > as the final step in curve creation..  I hope this was the
> > > > > correct
> > > > > > > assumption.
> > > > > > >
> > > > > > > Cheers,
> > > > > > >
> > > > > > > Terence Lowe.
> > > > > > >
> > > > > >
> > > > >
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > Yahoo! Groups Links
> > > > 
> > > > 
> > > >
> > >
> >
>