QTR-Quadtone RIP

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. 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. 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. 

--- 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
> > 
> > 
> >
>