Digital BW, The Print

> More simply:  if you know the exact spectral response of, say, the red
> element of a CCD sensor, and I tell you I got a red value of 130, can you
> tell me the original spectral input?
>
> Answer: no.

Jon,

I don't understand the relevance of that.  You do NOT have only the red
element (unless it's only red, that is), you have three values.  Also, I do
not see how knowing the exact spectral response of the CCD is required to do
this.  It IS one method, but, IMO, a poor one at best, as it adds another
variable that is unnecessary.

What you do is simply create a "map" for the RGB values to grayscale values
using a LUT.  The LUT is generated by taking a full spectrum image with both
the B&W film, exposed and developed as you like and the color film, scanning
the two films on the same scanner, and "matching" the graytones to the RGB
tones at the same point in the image.  Of course there is going to be some
error, but I believe the error is insignificant.

I do not believe this needs to be calculated, it can be, if the mapping is
deterministic, what is called, characterized.  If scanner differences are an
issue, you simply characterize this for the different scanner, following the
same procedure.  If you do it once, you can do it a thousand times, for any
combination of films.

Austin