There is a misconception about the overall color of color
negative films. I started to write something about this but
realize that I need to refresh myself because I am not coming up
with some details from memory. However, the color is NOT
constant, it is not an overall color correction filter, rather it
varies with the density of one of the color layer (maybe two of
them, this is one of the details I must look up). The idea is
that the dyes which form the image are imperfect and transmit
some undesired colors. This affects the purity of the reproduced
image. By using dyes that are themselves colored but change color
when affected by the developer, a reversed mask can be created on
the film which corrects for the spurious transmission of one or
some of the dyes. I must look up the name of the scientist at
Kodak who invented this system, its fallen off my memory. If you
look carefully at the image on a color negative you will see that
the amber color disappears where some other color appears. In
fact, it forms a reversed image. Masking for correction of the
color separation images on the film goes back before integral
multi layer color film. In fact, it can be used with B&W color
separation negatives to correct for the spectral transmission of
the camera filters and film. The filters can become quite
complex. However, it is possible by using the colored coupler
method in multi layer film to eliminate or at least much reduce
the need for this. The result is improved color purity and
saturation in the print. There are analogous masking methods used
in color reversal films but they use a different technology. The
overall color in the unexposed areas is because the maximum
density is actually shifted to a lesser density to allow the
reversed mask. This is not very intuitive but will become clearer
with some thought.
Colored coupler masking is explained in several standard texts.
Bob Kiss said something about reducing the complexity of
color correction filters. He may have meant masking filters
because color correction for an overall color cast is not the
same thing as masking.
I used to have a never-fail memory but as I get older I loose
more stuff. Sherlock Holmes addressed this in his very first
adventure telling Watson that he thought a man's memory was like
a little attic (box room) and, after a while, you have to take
something out for every new thing you put in. I think my memory
has an open door at the other end which is dumping memories into
the same space that lost nuts, screws and springs go into.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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