[pure-silver] Re: Kodak vs Ilford
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sun, 23 Mar 2008 17:40:50 -0700
At 05:19 PM 3/23/2008, you wrote:
Bob Pace, with 50 years of experience, years ago developed masking
techniques for "Gasper Color", which was the fore runner of Cibachrome, has
written a self published book "Masking for Photographic Processes" This book
is a very practical approach.
Knut Kvistad self published a book "Photocomposition, A reference guide"
This book gets into some of the more esoteric use of masking.
David Doubley self published a book "The Dye Transfer Process"
This book really explores the techniques of Masking
Howard Bond wrote a definitive series of articles for "Darkroom Techniques"
The collection presents a detailed discussion of masking in relation to
Black and white photography. A visit to phototechmag.com
Might be a source of reprints, and back issues of Howard Bond's articles.
Lynn Radeka wrote a chapter in "Way Beyond Monochrome" about masking
techniques, then he self published "Contrast Masking Kit" A compilation of
masking techniques and special procedures. Parts of this originally appeared
in Darkroom and Creative Camera Techniques 1989 issues July-August "Contrast
Reduction Masks", September-October "Shadow Contrast Increase Masks",
November-December "Highlight Masks" by Mark Jilg and Dennis McNutt. These
articles present a great overview with great photos.
David Malin wrote a ten page article in Kodak's "techbits" issue #1 1990 on
image enhancement using unsharp masks.
Barry Thornton's book "Edge of Darkness" chapter 13 "The Mask of Sorrow"
Eloquently writes about his experiences with masking.
These authors cover the subject well, from the very simple calibrated by the
eye ball method to the very exact.
Jonathan Ayers [mail1@xxxxxxxxxxxxxxxxx]
Thank you, I would not have remembered all these references
although I am familiar with them.
Masking for contrast reduction is relatively simple, relatively
being the operative adverb. If a linear material is used for the mask
the overall contrast is reduced but the actual curve shape of the
original can be changed by mask which is not linear in some fashion.
For instance, highlight contrast can be reduced without much
affecting the rest of the image by making a mask with relatively high
contrast and exposed so that only the highlight portion has much density.
There is another, and much more complex, system of masking used
for color. These masks are used to correct errors in the color
filtering of the original and the transmission of the dyes or
pigments used for printing. Modern color negative materials have a
self-masking system built-in. The masks are generated automatically
by using color couplers (the substances that become dye) which are
themselves colored. When the coupler is converted to dye it changes
color to the color required by the particular color layer. This
leaves a positive image in the mask color embedded in the color
image. The mask color is chosen to neutralize transmission of the
color of the image by spurious color transmission from the dyes in
other layers. Most color films contain colored couplers in two of the
layers. This is why the clear areas of the negative have an orange
cast. This method of masking is obviously not useable for positive
images for direct viewing although it _could_ be used for positives
meant only for duplication. Another, more recent method of masking
and one used in both positive and negative materials, makes use of an
interaction between layers. Development in one layer produces
reaction products which are allowed to migrate to adjoining layers to
affect the degree of dye generation. Some modern negative color films
make use of both methods.
The reason for this masking is that the unwanted transmission
results in the reduction of color purity and saturation. Very
elaborate masking was used for four-color photo-mechanical printing
to compensate for the ink spectrum. These masks are still used by are
now generated electronically.
I should also mention un-sharp masks. These are contrast masks
which are either exposed or printed in such a way (for instance
exposing and printing through the support side) that the mask image
is blurred. The effect is to lower overall contrast with little
effect on small details. This results in an enhancement of acutance
or edge sharpness so that textures, etc., look sharper. Since the
mask is less critical of exact positioning than a sharp mask the
method was quite widely used for Cibachrome printing.
Kodak used to make a special film for masking as a component of
their dye transfer method but all of the dye transfer materials were
discontinued several years ago. A good substitute is T-Max100 film
which can be very fine grain and has a suitable spectral response for
color work.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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