U of S | Mailing List Archive | alt-photo-process-l | Re: uncurve/curve comparison on Loris' website

Re: uncurve/curve comparison on Loris' website

Hi Katherine,

No problem—no need to apologize.

In a message dated 10/5/07 10:05:46 AM, kthayer@pacifier.com writes:

Mark wrote:

> My mistake then.  It sounds like you have been able to calibrate a 
> curve that works well for you.

Sorry, Mark, I don't always get your posts, so I have to go to the 
archives to see your responses and I don't always remember to do that.

Although the post of mine you referred back to wasn't about any 
specific curve of mine but was a general discussion about the 
tradeoffs involved in constructing curves for gum,   and although the 
general shape of the curves I generate is just as a curve "should" 
be,  I do appreciate your offer to diagnose any curve problem, and 
will be sure to take advantage of that kind offer in future if I 
think I  could use your advice about curves.  At any rate,  I figured 
out some time back that the problem was that the printer settings 
were wrong, as you suggested and as we've discussed.

But I need to say a word about that earlier post you referred back 
to:  I want to make sure everyone understands that I wasn't 
criticizing the curves that I was describing, that had been 
graciously sent to me by others; I was simply using them to 
illustrate the tradeoffs that must be considered when constructing 
curves for gum, that we all face.   My point was that with gum you 
always have tradeoffs.  Given a middling level of pigment saturation, 
you can have good separation in the midtones at the sacrifice of 
separation in the highlights and shadows, or you can have good 
separation in highlights and shadows, by sacrificing separation in 
the midtones.  The examples of curves I mentioned were from people 
who had elected for the latter option.  I don't think there's any 
right or wrong about which way to go;   I wasn't condemning those 
curves or those who created them for being "wrong;" I was only using 
them as an example of the tradeoffs that are necessary, whether we 
are conscious of them or not, and as a way of saying we're all in 
this difficulty together.

The comparison offered at the top of this thread serves as an 
illustration of the other approach, to concentrate on separating 
midtones and let the highlights and shadows go, although in this case 
the difficulty about highlights and shadows was apparently resolved 
by pushing most of the outside values, the shadow  values 
especially,  into the midtones (I'm speaking absolute values here, 
not relative values, and print tones rather than negative 
densities).  As I said, I don't think either approach is right or 
wrong, they're just different ways to deal with the same problem. I 
would probably approach that image differently.  I wouldn't lighten 
the shadows, because the print isn't too dark overall,  in the sense 
that I mean by "too dark" (and that I illustrated in the print that I 
showed).   In this print it's mainly the midtones that are too dark;  
the shadows are fine right where they are.  I like the tires still 
black but somewhat lighter than the darkest tones, as they are in the 
"before" print, and would want to keep them there rather than to 
lighten them into the midtones.    But, that's neither here nor 
there, because it's a very subjective call and as I've said, there's 
no right answer.

As I said before, I find the effect interesting, and  the comparison  
useful as an example of two very different ways to print the same 
image.  But I don't find it compelling as proof of the superiority of 
a particular approach to curves for tricolor printing, since the 
"after" print has a pronounced color cast  and doesn't cover a full 
tonal range (in the absolute sense rather than the relative sense; in 
other words to my mind a good set of tricolor curves, for an image 
that includes a full tonal range as it appears this one does, should 
result in a print that also includes a full tonal range, including 
shadows that run from, say reflection density 1.40 or so to .9 or so, 
and highlights that run from say .20 up, as well as a full range of 

The tradeoff I discussed above holds for fairly common mixes of a 
middling color saturation; different mixes introduce different 
tradeoffs, as there's a complicated interaction between negative 
densities and pigment saturations as they affect print tonalities.

As for tricolor, my calibration for each of the pigment mixes I'm 
using in my current explorations of tricolor (Prussian blue, PV19 
gamma, and PY97) found the curves all the same, a deep curve that 
looks identical across the three pigments, although I haven't 
superimposed them to make sure they correspond at every point.     My 
study of curves and pigments  suggests that differences in curves are 
more a function of differences in color saturation than of the colors 
per se; a less-pigmented mix generates a shallower curve than a more-
pigmented mix of the same pigment; a less-saturated color generates a 
shallower curve than a more-saturated color, regardless of the 
pigment.  So it makes sense that since I use my colors for tricolor 
in equivalent saturations (note, I don't mean equal pigment 
concentration; I mean equal color saturation, which is something 
different) in order  to ensure color balance,  that the curves would 
be the same.  Whether these curves work well for tricolor is yet to 
be seen, since I haven't had a chance to print those separations yet, 
and since as I keep saying, tricolor is more a matter of how the 
layers interact than of calibrating the individual layers.

Looking back over this thread on the archives, I see I owe you an 
apology, Mark; you weren't the first person to drag my curves into 
this thread that I thought had nothing to do with me.  There was an 
earlier post I hadn't seen before, that addressed me by name and 
stated rather imperiously  that my curves, or the system I use to 
calibrate my curves, must be wrong.  That post also suggested that my 
purpose in posting the two prints I posted in another thread was to 
show that curves are worthless or useless, which of course is just 
silly.  If I thought curves were worthless or useless I wouldn't have 
undertaken a study of curves as part of my ongoing study of negative 
densities and pigment concentrations as they affect print 
tonalities.     The two prints were posted in a lighthearted 
expression of solidarity with a person who was struggling with curves 
for tricolor gum, and if there was a point I intended  to illustrate 
with it, it was simply the point that what works for three separate 
layers doesn't always work for three superimposed layers, and that 
what we need is a three-dimensional calibration.  The comparison was 
simply posted as a sharing of work in process between friends; I'm 
sorry it was misinterpreted by others.

On Sep 30, 2007, at 4:59 PM, Katharine Thayer wrote:

> Mark wrote:
>> Maybe I misunderstood one of your ealier posts.... I don't have 
>> time to search back right now for it, but I thought you had been 
>> working on a calibration and the results had been what seemed to 
>> be ok differentiation in the deep shadows and highlights, but very 
>> flat midtones.... I thought if you could post what the curve liked 
>> like when shown in the Photoshop Curves Window that it would be 
>> helpful to see what is going on.  Usually you can tell by the 
>> shape of the curve what the problem is.
> Yes,  you did misunderstand completely.  That was in a different 
> thread altogether;  I was discussing curves for gum in general, and 
> to illustrate a point, I was describing some curves and charts 
> people have sent to me over time as examples of "good" gum curves, 
> that fit that description.  They were generated, actually, from the 
> PDN system (although I didn't mention that because I didn't think 
> it was germane to the discussion).   But no, I wasn't describing 
> any curve of my own, nor do my curves fit that description.
> kt

Best Wishes,
Mark Nelson

Precision Digital Negatives - The System
PDNPrint Forum at Yahoo Groups

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