Re: Best CI for process

From: Eric Neilsen <e.neilsen@worldnet.att.net>
Subject: RE: Best CI for process
Date: Sat, 01 Oct 2005 21:35:38 -0500

> This was quoted from the site referenced by Michael. Perhaps this is the
> problem when talking about exposing prints. What is useful in silver
> printing is not the same as what is useful for platinum printing. The
> straightness of the line may differ but the underlying theme of useful
> remains.

The measurement technique for CI is a bit more complicated than that
for gamma or average gradient. Criticizing the complexity of this
process doesn't help at all because, roughly speaking, the CI was
introduced as a more universally applicable measure of contrast for
negative materials. Measures like gamma can certainly be used for
graphic art material, for example, but the numbers wouldn't compare
very well across different classes of emulsions. CI was aimed at
broader applicability rather than simplicity of calculation.

One may be able to come up with a simple measure of contrast, speed,
etc. for a particular application. For example, log exposure range is
a useful measure of contrast for b&w print emulsions because Dmax is
pretty much the same for a particular surface. (This, of course,
wouldn't be the case if the emulsion has pronounced toe or shoulder,
as in old time emulsions.) One can find CI for printing emulsions but
there is not very much use to do so, unless you are interested in
comparing contrast of paper and other emulsions. Indeed, as far as I
know, CI is not very widely used outside Eastman Kodak Company. Recent
ISO standards are often written in spirit of gamma (slope of framing
line of a D v. log E curve) or average gradient.
Received on Sat Oct 1 22:15:59 2005