From: Michael Healy (mjhealy@kcnet.com)
Date: 01/27/03-05:45:39 PM Z
I was referring to Charles H. Palmer's article, "Digital negatives for
alternative processes", which forms chapter 17 of John Barnier's "Coming
Into Focus". Palmer's emphasis is platinum only, and his essay addresses the
problems of working with a service bureau. I tackled the article despite the
fact that I am not doing platinum, and am trying to make my own here at
home. Since the exercise was worth the considerable trouble involved, I will
go into a bit of detail regarding my process. Others may read this and be
able to describe these steps in better (or more accurate) detail. I am happy
to stand corrected if need be.
The problem as I understand it, in a nutshell, is the "curve" so many people
keep talking about. This curve runs from 0% in steps of gray by 5%
increments of 5-10-15% up to 100%. If you print this out or eyeball it on
your PC screen, it will show the shades of gray in incremental grades. This
is the curve you're messing with when you go into PS and do
<image><adjust><curves>, and start pulling that diagonal line around with
your cursor. There you are altering values either intuitively, if you
understand the process, or randomly if you're like me. Palmer's is a way to
manipulate these increments SYSTEMATICALLY. His approach is to make test
curves, evaluate them in actual prints, and then use these results to create
your own adjustment curves, whcih you apply to your PS negs before printing
to acetate.
A real problem, by the way (also addressed by Judy Seigel this date), is
that you are dealing with so many variables. Your acetate sheet may be
Pictorio or it might be Probilemico. Plus you've got inks involved. And
finally, there are the coating and the papers. A single neg can't address
all of these in the same way. Burkholder argues, in fact, that with curves,
you can conceivably create a platinum neg, a cyanotype neg, and a kallitype
neg, all from the same scan.
About Palmer: his Fig. 4 (p. 233) lays out fourteen different manipulations
of the standard curve. (This curve, by the way, is on the CD that comes with
Burkholder's book. Copy it down to your PS directory and give it a name such
as "Curve_default".) I will give you two of Palmer's 14 deviations from the
0%-100% "default". He labels these "D-max 0.5" and "D-max 1.8". Below are
the new values he gives to the default. Bear in mind that the left column
(default) **is** a correct distribution of gray from white to black...
0%-----31%---1%
5%-----36----2.1
10%---39----3.1
20%---44----4.4
30%---49----6
40%---52.5--8.3
50%---57.5----12
60%---63.4----16.9
70%---68.4----24
80%---73.4----32.5
90%---80.6----45
95%---89.9----62
100%-100.0-100.0
If you make your own curve called D-max 0.5, you can save it in PS (see
below), and apply it to any image you want. By that I mean that the values
will simply be converted systematically as an equation, rather than as a
result of your jerking on that graph line, trying to figure out why they
want you to do that.
An example: Say you create one and apply it to your image (D-max 0.5, the
one from 31%). PS will find all pixels that currently report 0% black
(white), rewrite them to show 31% black (light gray). Then it will find all
5% (faint gray) and convert them to 36% (a light gray that's somewhat darker
than your 31% that was all white). Etc. Now make another new curve and apply
it to another copy of your image (D-max 1.8, the one from 1%). This time PS
will rewrite all 0% to 1% (not much change), 70% to only 24% (a very light
gray), etc.
What you can do is get Burkholder's DEFAULT curve file, and make a few of
these curves. Save the default a number of times times, each one for a
different curves. You end up with "x" identical Burkholder files, w/ names
of <default>, <0.5>, <1.8>, etc., all following the curve names in Palmer's
Fig. 4. Now create actual curves modeled after Palmer. This is done in
<page-setup><transfer fuctions>. Here you get that graph again, but you also
get empty boxes for each percentage increment. You fill these out and then
save this as a curve. Now go back to the Burkholder file. Call up each copy
and actually apply the appropriate curve to it. Dump all of these
manipulated curves (and also the unaltered <default> curve) into one 8x10 PS
file, and print this on acetate CONVERTED TO A NEG, not printed as a
positive. Now put that "neg"in your contact printer and print the sheet
onto your paper like it's a photograph. You'll need to print a few test
strips until your exposure actually gives you d-max that's black (or blue in
the case of cyanotype). Then print a full-size copy that shows all of the
curves together. One of these will print a range of white to black with the
best separation. It may be the default curve, but more likely it will be one
of the others or some combination. After that, you work backwards to adjust
the values of your adjustment curve in relation to the values for this
"good" test curve. Burkholder (p. 191) gives details on how to make these
final adjustments.
Mike Healy
----- Original Message -----
From: "Leonard Peterson" <windpoint@hotmail.com>
To: <alt-photo-process-l@skyway.usask.ca>
Sent: Monday, January 27, 2003 2:09 PM
Subject: Re: Curves on home-brewed digital negatives-Mike Healy
Mike, What are you referring to in your message "Palmer's 14 "test
correction curves" (Barnier,
>p. 233)"? Thanks from a novice in this world. Len
>From: Michael Healy <mjhealy@kcnet.com>
>Reply-To: alt-photo-process-l@sask.usask.ca
>To: alt-photo-process-l@sask.usask.ca
>Subject: Curves on home-brewed digital negatives
>Date: Mon, 27 Jan 2003 13:05:07 -0700
>
>
>----- Original Message -----
>From: "H. Lee Pratt" <squnch@cox.net>
>To: <alt-photo-process-l@skyway.usask.ca>
>Sent: Monday, January 27, 2003 11:25 AM
>Subject: Re: introduction and request for info on digital negatives
>
><snip>
>
>Second: I too have an Epson 3000, which I have dedicated to b&W work,
>using the PiezographyBW drivers and inks. My understanding at this
>point is that you only need a "curve" if you are making a contact
>negative through a service bureau = using lithographic film. I doubt
>you will need any curve to make a desktop negative on your Epson, as
>you can simply invert your final image to a negative and print it to
>your 3000 on Pictorico OHP film. (Epson transparency film does not
>work, but the Pictorico product does.) If your positive looks good on
>the screen, the negative will probably print well on #2 paper.
>
><snip>
>
>I am inclinded to disagree with you about curves on desktop negs. I also am
>new to making my own desktop negs, but here's what I find: the same neg
>does
>NOT give the same printing outcome with argyrotype that it gives me with
>cyanotype. Different processes, different papers, so maybe it should be
>self-evident. Definitely not the same results at all.
>
>What I did when I first started this homebrew negative stuff was to input
>(in Photoshop) every one of Palmer's 14 "test correction curves" (Barnier,
>p. 233). Then I applied every one to a different copy of Burkholder's
>digital step tab. Finally I copied all of these onto a single 8x10 PS file,
>which I printed on acetate. If you do that, and print with this, I think
>you're going to be in for a surprise. It was a really tedious project, but
>there is no better argument for the need of curves on your desktop negs.
>
>Mike
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