Digital BW, The Print

CCD's and film are energy detectors - their response is directly 
proportional to the incident energy in a given frequency range. 
Different types of sensors/film, X-ray, UV, IR etc. are sensitive to 
different frequency ranges. Imaging radar, MRI, etc. perform the same 
function except they are active and the processing of the returns 
measures the energy profile to produce an image.

Film, CCD's, etc. are not coherent in that they don't record any phase 
information. RGB channels are nothing more than the energy in three 
bands of the spectrum. The only way you could not reconstruct the 
intensity of white light would be if there was a frequency that fell 
outside the passband of all three of the RGB filters. This is the key 
question. Otherwise the RGB output can be calibrated to produce a 
equivalent gray scale of any film if you know the characteristics of all 
the sensors involved. There are some questions in my mind about fidelity 
of this conversion. How does the noise floor of the combination of the 
three filters covert to the noise floor of the gray scale generated from 
the RGB conversion compare to the noise floor of the same image taken 
directly on a intensity only (B&W) gray scale sensor?  I consider that 
the real question.

Truman

Austin Franklin wrote:

>Anthony,
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>>    
>>
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>What, precisely, does B&W film "sense"?  What "information" is recorded on
>B&W film, and what information do the scanned values 0-255, let's say, give
>you?  NOTHING but intensity, period.  That's it.  Light to dark.
>
>How is this information derived from the original "scene"?  Both the film,
>and the CCD, sense the number of photons that "hit" it.  They are spectral
>independent.  Look at the film response curve for B&W film.  It's reasonably
>flat, up to the point of fall-off.  That means that all photons, no matter
>of what frequency, are treated, for all practical purposes, equally, and
>generate the same results on the film, recording the average intensity of
>light at "that" point in space.
>
>Now, does the RGB data not have this "intensity" information?  How accurate
>can you extract intensity from the three RGB values?  Does it matter that
>different combinations of RGB produce the same intensity?  Only if that's
>not how the B&W film would have seen it as well...which, is why different
>colors produce the same results on B&W film...so the answer seems to be no,
>it doesn't matter.
>
>Austin
>
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