Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Anthony 
Atkielski" <anthony@a...> wrote:
> Clayton writes:
> 
> > It's a subject that has concerned me for a
> > long time, as I've hinted at in past posts
> > about my fear of losing the look and feel
> > of particular films.
> 
> I worry about it, too.  There is a very widespread but mistaken 
belief that
> the images produced by any B&W film can be duplicated by some magic
> manipulation of a color image in Photoshop.

Why should this be so hard?   Every black and white film has a 
characteristic response curve, and that curve can be characterized 
for R, G, and B (because even modern "panchromatic" films are not 
perfectly panchromatic).    So if you start off with a wide-latitude 
color film, like Portra, what limitations do you bump up against 
trying to simulate a given B+W film? 

It seems like all you have to do is compute a scalar from your 
source (color film) response curve to your target (B+W) response 
curve for each intensity level.   When you're done you have a vector 
of scalar values and that vector is the curve you use for your 
conversion.    What would NOT be described by that curve?   It would 
tell you how much shadow detail you get, how highlights look, how 
smooth or even midtones are, etc.