Digital BW, The Print

Anthony,

> > Every black and white film has a characteristic
> > response curve, and that curve can be characterized
> > for R, G, and B ...
>
> No, it cannot.  The curve is just that: a curve.  The RGB values are just
> three numbers--equivalent to three straight lines of different heights in
> the spectrum.

Huh?  And yes, it can be characterized, to some degree of accuracy.  To
characterize it for RGB, you would use THREE curves, one for each color, not
just three numbers!

> All the rest of the curve between those three lines is lost
> when a picture is taken in color.

I don't believe you know what you're talking about.  The three colors (which
are actually CMY), have overlapping regions.  They are not brickwall
cutoffs, they taper off on the ends.  They in fact DO encompass the entire
spectrum that B&W film does as well.  The spectral response of Portra 400VC
is 375nm to 680nm.  The spectral response of Tri-X is 400nm to 650nm.  So,
in fact, Portra has a higher spectral response.

If the spectral response of your color film encompasses that of the
grayscale (which it does), and the film response is deterministic (which it
is), and the conversion to RGB is also deterministic (which it is, and vice
versa), then it can be characterized.

Like you said, this is not mystical, it is purely good science, and
obviously an understanding of how this really works without simply guessing.
The operative words being good, understanding, and not guessing.

Austin