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From: jer@peora.UUCP (J. Eric Roskos)
Newsgroups: net.rec.photo
Subject: Re: Product Quality: Color prints from slides
Message-ID: <1750@peora.UUCP>
Date: Sat, 26-Oct-85 21:41:15 EST
Article-I.D.: peora.1750
Posted: Sat Oct 26 21:41:15 1985
Date-Received: Mon, 28-Oct-85 03:28:13 EST
References: <298@tekig4.UUCP> <349@vaxwaller.UUCP> <5746@tekecs.UUCP>
Organization: Perkin-Elmer SDC, Orlando, Fl.
Lines: 51

> Reversal color print processes are not as good as negative print
> processes. MY OPINION: Don't bother to flame if you disagree!

Why would anybody flame you! :-)  After all, it's true...

Color rendition in prints from color negatives is better than the color
rendition in prints from slides.  This is because present-day dyes
have "tails" on their spectral absorption curves that overlap the
spectrally-absorptive regions of the other dyes.  This is particularly
a problem for the cyan layer, and to a lesser degree, the magenta layer.

The result of this effect is a color "impurity" in the negative image,
typically a red impurity in the cyan areas, and a yellow impurity in the
magenta areas.

To correct for this, color negative films have a yellow and a red color
mask whose color is decomposed in proportion to the presence of the
corresponding impurity.  Thus in an area with a large yellow impurity, the
yellow mask will be almost completely decomposed, i.e., the yellow mask
goes away, to be replaced by the yellow impurity.  Likewise for red.  The
result is that the film has a uniform yellow-red cast to it, rather than
having a red cast in the cyan areas and a yellow cast in the magenta.

However, with slide films, this can't be done, since the slide is intended
to be viewed by projection, and a yellow+red cast (well, possibly the
complementary colors for a reversal film) would be unacceptable, whereas
when printing from a negative this can be corrected with color correction
filters.  Thus, so that the whites will be white on a slide, the other
colors have to be compromised slightly in the print.

This is why color negative films exist.  (Well, also because the processes
to develop them are simpler.)  Contrary to popular opinion fostered by the
fact that photojournalists and others who intend their photographs to be
reproduced by ink printing use slides (and the biased editorial position
of some popular photography magazines), the color rendition of color negative
films is "truer" than for slide films. It should seem intuitively probable
that a film that is *designed* for making prints would be better-optimized
for making good prints than a film that was designed for making slides
which are occasionally printed.

On the other hand, grain is marginally better in Kodachrome.  It's my
personal feeling that image sharpness is not sufficiently good with 35mm
cameras to make that much of a fuss over grain (eventhough I do use
a very fine-grain B&W film myself!) when comparing an ASA 100 film with
Kodachrome, and they don't make Kodachrome for larger-format cameras.
-- 
Shyy-Anzr:  J. Eric Roskos
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