Digital BW, The Print

Hi Truman,

> CCD's and film are energy detectors - their response is directly
> proportional to the incident energy in a given frequency range.

Correct.

> 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.

Agreed.

> 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.

Agreed.

> 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.

Well, that's what I'd like to believe...  I'm sure that somewhere along the
spectral curve that the response needs to be "adjusted", as there is
sensitivity falloff at the ends of each colors response curve.

> This is the key
> question.

Exactly.

> 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.

BINGO.

> There are some questions in my mind about fidelity
> of this conversion.

It's a concern, certainly, but I'm not sure it's significant, given,
remember, we are only sensitive to around 100 gray levels anyway...

> 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.

Let's say it's insignificant, for arguments sake.  So, I take it you now
agree that:

1) B&W film merely records intensity only, and has no spectral "influence"
(that can't be corrected)
2) That RGB data contains this intensity information (to within a degree of
accuracy, of course)
3) That the same (to within a degree of accuracy) intensity information that
would have been "seen" by the B&W film can be extracted (with appropriate
LUTs to correct for "distortion") from the RGB data?

So, if this is true, then two questions remain...one I've incessantly asked,
with no response...

1) Is there any frequency in the B&W film's response range that is not
covered by the RGB response range?

2) Characterizing noise/distortion, and can it be corrected such that the
grayscale image is "replicated"?

Regards,

Austin