Digital BW, The Print

Hi Kevin,

> Thanks for the detailed answer.  I'm not sure if you are agreeing or
> disagreeing though :)

Agree in conclusion, but I think you were missing some details there as to
how things work.

> After reading your response I think I can still say development times
> are 'mostly irrelevant'

Hum.  If you use N+- exposure to compress/expand the scene density onto the
film, you have to use N+- development...

>  From a purist perspective getting the largest density range on the film
> is best because your scanner produces more discernible data.

Correct.

> >> By setting the black point, setting the
> >> white point and scanning the negative am I not mapping the entire
> >> density range of the image to a numerical range of 0-256 or 0-64k?
> >
> > Not quite.  The setpoints have not a thing to do with the scan.  They
> > are
> > applied to the scanned data AFTER the scan occurs.  I believe that's
> > actually not the right question.
>
> OK, it makes sense that the set-points are applied after the scan.

That is true of the consumer scanners you and I use.  There are some
scanners, and I've designed one, that have analog gain control between the
CCD and the A/D, and has, basically, hardware setpoints.

> Cool, thanks for the primer.  Wouldn't the software use some algorithm
> to interpolate values for the gaps instead of leaving them empty?

That is a good guess, but no...remember, every pixel has a value associated
with it.  What are you going to interpolate?  If you did somehow
interpolate, you are giving data that was the same, different values, or
creating NEW data that didn't exist before...  The gaps really don't mean
anything, as you are taking the N bit data and converting it to CONTINUOUS 8
bit data...in other words, when you go to print, you DO have every data
value from 0-255 (or most every one).

> >> This mapping would take place independent of the absolute density any
> >> particular zone.
> >
> > That is true.  There is no directly calibrated correlation between
> > scene
> > density, film density and scanner value....unless you went out of your
> > way
> > to calibrate it...which is really unnecessary, as doing so won't get
> > you
> > better scans.
>
> Agreed.  So can't I conclude that the value of the slope of the
> exposure density curve is (ignoring the number of gaps) irrelevant to
> the scan?

If I understand you correctly, the answer is yes, it is irrelevant, as long
as you have enough data there...as the slope approaches 90, you have less
data points per delta.

> OK, the greater the density range of the film the more discernible
> data.

Correct.

> So couldn't I just settle on an N+1 time or N+2 time as long as
> the resultant film density doesn't exceed the optical density range
> of my scanner I should be OK. Yes?

I am confused as to why you think you always would use +
exposure/development.  + is for expansion of low contrast scenes (small
density range) into the higher density range of the film...and - is for
contraction of a high contrast scene (large scene density range) into the
smaller density range of the film.  There are circumstances in the real
world where you would use either.

Regards,

Austin