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From: bhuber@sjuvax.UUCP (B. Huber)
Newsgroups: net.rec.photo
Subject: Re: Re: Product Quality: Color prints from slides (contrast buildup)
Message-ID: <2474@sjuvax.UUCP>
Date: Mon, 28-Oct-85 16:24:48 EST
Article-I.D.: sjuvax.2474
Posted: Mon Oct 28 16:24:48 1985
Date-Received: Sat, 2-Nov-85 00:17:27 EST
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Organization: St. Joseph's University, Phila. PA.
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> Something which has always bothered me, when you copy a print onto
> a slide (an perhaps other copies as well) you get 'contrast buildup'.
> It seems to me that if the contrast range of the print is *less*
> than that of the original subject, then the contrast range of the
> slide should also be *less* than the original.  So why does the
> slide show *higher* contrast?
> 
> E. Michael Smith  ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems
> 
The contrast range of a medium basically is the difference between its 
blackest black and its whitest white.  Actual scenes can have an apparent
range of over 10 f-stops; the greatest range typically available on B&W
paper is about 7 stops.
The photographic process reproduces images, then, by "squashing" the grays:
differences between grays are understated in the image.
A contrasty image is one, then, which represents a fairly small range of
grays with its full black-to-white spectrum; a noncontrasty image will
reproduce a wide range with nearly uniform gray.
To answer your question: The contrast range of the slide is (except
in extremely exposed cases) constant for all subjects; what concerns you
is the relation between a given contrast range in the subject and the range
of brightnesses with which that is reproduced.
Think of it like this:  a demagogue will reproduce ideas as either black or
white, with little gray in between.  A sophist will never use either extreme;
everything is just shades of gray.  The demagogue's black isn't really blacker
than the sophist's; nor is one's white really brighter than the other's.  What
differs is how they compress or expand the ideas in the middle.  The former
is contrasty, the latter far less so.