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Multiple Colored Desktop Negatives
Sorry, this is long...
For anyone who has not read Dan Burkholder's excellent book
the following may not make much sense. Among other things,
Dan discusses replacing the colors in an image when making a
negative off a desktop inkjet printer. The basic idea is
that we don't need full density from all 4 colors of ink in
order to achieve sufficient density for use as a negative
for alternative printing methods. By replacing black with
the appropriate shade (a reddish/orangish tone) problems
with ink puddling and running can be reduced on plastic
transparency materials, and the need for an adjustment curve
is reduced. The Color Table in Index Color Mode of
PhotoShop is used to achieve this with relatively little
pain and agony.
In trying to get calibrated for making gum prints I set out
to do a bit of testing in order to find the most appropriate
color to use with my materials and methods. I made a series
of graduated bars, each one of a different shade. For each
shade I made bars at 0%, 10%, 20%, 80%, 90% and 100% on a
grayscale before converting to Index Color. I then printed
the desktop negatives with exposure time increasing along
the bars. Picking the right printing time is simple: look
for the first patch at 100% (clear film) with maximum black,
6 minutes in my case. Picking the right shade is more
complicated.
The problem I have found (as described in a post several
months ago) is that there is not enough separation in the
shadows, and too much separation in the highlights. I can
find a shade (call it Shade A) which just barely maintains
paper white on the 0% bar when printed for 6 minutes. But
the 10% and 20% bars are too dark, and the 80% and 90% bars
are almost as dark as the 100% bar.
The obvious solution is to apply a curve in PhotoShop before
printing the negative (using a single color). But the shape
of the curve needed (at least in my case) is fairly radical,
which results in ranges of tones being compressed
(posterized) and loss of detail.
The idea strikes me: why use a single color and apply a
curve for making the desktop negative? Why not use the
Color Table to assign different shades to different tonal
values and let PhotoShop interpolate the appropriate shades
in between? For instance, when printed at 6 minutes I can
find Shade B for which the 100% bar prints at the correct
tone to look like it should be 20% (a near-highlight value).
I can also find Shade C for which the 100% bar prints at the
correct tone to look like it should be 80% (a near-shadow
value). So use the Color Table to assign Color A to 0%,
assign Shade B to the 20% point, assign Shade C to the 80%
point, and assign pure white to the 100% point. Maybe I
need to use more points to break up the curve, I don't know
yet. This will automatically invert the image into a
negative, as discussed in Dan's book.
Another advantage to this method is increased control.
PhotoShop only lets you select curve points at 0%, 5%, 10%,
20%, 30%, etc. for a total of 13 points on a curve (if you
enter them manually). With this variable color method you
could potentially have 256 different points on a curve, if
you had the patience to figure them out!
I grant, this is more complicated than applying a curve and
printing in a single color, but it could avoid some very
real problems. Anyone tried anything like this? Any
comments?
Garet Denise
Garet@Cornerstone-Inspection.com