QTR-Quadtone RIP

--- 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
> > > 
> > > 
> > >
> >
>