Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington>

 
> The part I think you are missing is that given a particular
> triplet of RGB densities you are NOT trying to go back to a
> "unique point on the spectrum".   The light in a real scene that
> exposed that point in the film is NOT one unique frequency.
> Every single point is composed of the entire  visible spectrum.
> You'll have an amplitude (probably different) for every single
> frequency.   The three density numbers can't possibly tell
> what all the amplitudes of all the frequencies are.  Sure it
> tells you a fair amount about the general shape, and it's close 
> enough for the human color perception.  But B&W film with a 
> colored filter can be much more selective about what 
> frequencies to be sensitve to and what ones not to be.  How
> dark each piece of file gets is based on integrating over the
> entire visible spectrum of the energy * filter * film sensitivity.
> One RGB triplett just doesn't have enough information to
> do that integration.

But the practical question in this discussion is whether it's good 
enough.   What Anthony has not established is that there is any 
PRACTICAL significance to that.   

When I have a point to make here I do some tests and scan in the 
results and post them. You can see them on my website.   Anthony 
could save us a lot of bandwidth if he would do the same.   

I'm an engineer and we have a motto: "The difference between theory 
and practice is a lot greater in practice than it is in theory."