QTR-Quadtone RIP

Andrew Maier <andrew@...> wrote:

> **
>
>
> ...
>
>
> > Create ICC-RGB ... allows you to drop a Photoshop image adjustement
> > curve into the ICC as well as the linearization data. See
> > http://www.paulroark.com/BW-Info/Embedding_Photoshop_Curves_in_ICCs.pdf
> >
> >
>
> One question, embedding the Photoshop curve, will I still be able to use
> the ICC profile to print from any software, or will this become a Photoshop
> only ICC?
>

I believe the ICC is usable with other applications.  That is one reason to
use Create ICC-RGB.  It's compatible with most applications as far as I
know.



>
>
> > ... my blacks seem to saturate off at about the 85% mark, ...
> > >
> > You can control that with the PS curve you embed in the ICC or with a
> > profile you make for QTR. If the 21-step with no curve hit its dmax at
> > 85%, then have a curve that ends at 85% on the black end of the curve.
> > Then look at where the inks are and how the R, G and B curves will affect
> > the C, M and Y inks. That will give you the control you need. Start with
> > the 50% patch and points on the curves at that input level. When you get
> > the 50% tone right, go to the 25% and 75% points. It's a iterative
> process
> > (aka trial and error, but you'll probably get the hang of it after a few
> > moves).
> >
> >
> So the process would be the following.
>
> 1. Create a curve where the black endpoints end at 85%, that is the curve
> is still linear (less steep curve), but black ends at the 85% level
>
> 2. Reprint the 21-Step wedge using Photoshop, thereby applying the curve to
> reduce, the ink output at the high end.
>
> 3. Remeasure with the spectrometer and use the output from the spectrometer
> + the applied curve to create a ICC?
>

Yes, in effect.  The linearization is automatically done by Create ICC-RGB,
but the print tone control is something you do by altering the points on
the curve -- the same on that ends at 85%.  Just print 21-step test strips
with the PS curves until you get the print tones right (and Lab L curve
reasonable).  Then use that as the final PS curve and use the Lab L from
that test strip for the linearization.



>
> This will cause a problem, as now with CS6, Photoshop (at least on the Mac)
> will not allow to print anything unmanaged. I will have to assign a colour
> profile.
>

The PS working space should be Adobe RGB (1998).  The print driver is set
to ICM/No Color Adjustment, PS is set to PS controls colors, and the Adobe
RGB (1998) profile is put in the profile box.  That, at least, is what
works with CS5 and Windows.  If the working space and profile are the same,
I believe the file's values will be un-altered.  (Once the ICC is done, it
works with grayscale files.)


> ... what do I do with the colour
> channels? Do I measure the a* b* values and try to minimize them, or what
> is the aim here?
>

You'll have to determine what look you want.  For a neutral looking print,
keeping the Lab A about the same as the paper base usually works.  A slight
rise -- one unit -- will give you more of a "selenium" look.  I would try
to keep the Lab A values from dipping too much at least through the
midtones.

For a neutral print Lab B also would be flat with a paper that is not
filled with OBA's.  If the paper base is cold, a straight line from the
paper base to the deep shadow values will look neutral/cool.

Obviously for warm you'll want an elevated Lab B, and a Lab A rise will
give more of a red-brown warmth than the yellow Lab B.



> So I would start to would take the 50% patch, measure it's
> Lab values, before and after applying the curve
>

Once you print with the curve ending at 85% (where the dmax will hopefully
be at the 100% patch then), you might want to measure the entire 21-step.

I like to open the file in Excel and graph it (insert line chart).  Graph
the Lab L in one "chart" (Excel terminology) and Lab A and B in a second
chart.  In the Lab A and B chart, I like the vertical scale to be a total
range of 10, with one unit steps.  Excel will default to a range that is
just enough to cover the measured values.  You'll drive yourself crazy if
you try to control the tones down to small percentages of one unit.

By the way, for the curve that stops at 85%, use the R, G and B curves
individually.  It's those individual curves that you'll be manipulating.

When you have the graph of the tones of the straight line 0 - 85% curve,
you can move more points than just the 50%, but moving that one will move
the others also.  So, it's not a bad place to start.

One thing to consider is that if the tones are just right at some point(s)
of the curve, nail those down by putting a point there, so that it will not
be altered when you move other points.

Hope this helps.

Paul
www.PaulRoark.com


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