Digital BW, The Print

Hello Anthony,

The spectral response of BW film is a fairly simplistic curve
that 'could' be somewhat represented by three points .

Here is one for PlusX125  ( really favors Blue )
http://www.kodak.com/global/en/professional/support/techPubs/f4018/f009_0431ac.gif

Here is one for Porta400  ( much more linear )
http://www.kodak.com/global/en/professional/support/techPubs/f4012/f009_0390ac.gif

Here a typical RGB filter set ( this one needs an IR filter )
http://www.edmundoptics.com/images/IOD_Product_Images/4726.gif

Assuming the CCD system is properly calibrated, I think it would
be possible to reshape a white reference to enhance the blue end
of the curve and get a close PlusX BW response when extracting a
luminance layer. Porta400 might need a little push in the red.

Am I missing something ?  BW film is not particularly frequency
selective and it will respond to single frequency energy in
pretty much the same  manner as a digital CCD. In astrophotography,
a spectrometer can be used to spread sometimes quite specific
wavelengh energies across a strip of BW film. The BW film has
no problem seeing the bright and absorbtion regions from IR to UV.

I agree, a green laser and red laser would show as two points on
a spectrometer, the eye resolves the mix as if it was a single 
yellow value. The BW film is just going to create a grey shade
based upon its spectra sens of those freqs as will the 'colorized'
CCD, but a luminance response is just the integration of the 
RGB levels.

OR, in retrospect, perhaps the film curves subtile sensitivity
curves Illustrate Your Point of not being able to reconstruct
them perfectly with 'three points' .... ???

Best,
Alex



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Anthony
Atkielski" <anthony@a...> wrote:
> You've got it!  That's exactly the problem, and that's why you can never
> simulate the response of one film or sensor using data from another
film or
> sensor.  You can't get a Tri-X look from a digital RGB sensor, and
you can't
> get a Velvia look from a Provia scan, and so on.
>