Digital BW, The Print

Austin,

I know you've said this before, and I'm sure we may have discussed it before
(if so, I forgot!) but do you have examples of which scanners might do it
like this? (tonal corrections in high-bit data, then convert to low-bit
data)

I did do some tests on this - can't remember now if it was with the Nikon
Coolscan 3 or the 4000, but I found that (whilst Nikon claim they do tonal
corrections in high-bit) doing any kind of end-point adjustment resulted in
substantial combing in the histogram. I think it was during that process
that i also found out that NikonScan's histogram display was also
exceedingly unreliable - displaying 'substantially' different data even
after a full scan and save ... compared to after reopening the scan file.
(in other words both at times when one would expect the software to be able
to correctly count ALL pixel values... rather than speculation based on a
preview scan.

My sense tells me that scanners should be set up something like this:
Light source -> Film -> Sensor -> 'x'bit ADC -> Data 'tonal' adjustment ->
Convert to output bit depth -> out to computer

Where 'data tonal adjustment' would be using some kind of Look-Up-Table or
function to convert incoming raw data to corrected value... and 'Convert to
output bit depth' which converts high bit data to 8 bit if appropriate.
There must also be some additional steps I would guess, to combine colour
data etc for a mono scan (not in the Leaf case, I know!!!), but I am looking
for the essentials!

Would that be about right on flow? And if so, what would your estimation be
on what Nikon might have done that could result in combing on tonal
adjustments?

I should add that I haven't tested this in a while (so perhaps later version
of NikonScan resolved things), but I do not believe that I was mistaken when
I did my tests ;)

Nij



> -----Original Message-----
> From: Austin Franklin [mailto:darkroom@...]
<snip>
> Here's one of the rubs of this issue.  If you select 8 bit data from the
> scanner, the scanner driver typically does the tonal corrections
> TO high bit
> data, then converts the high bit data to 8 bit data and sends you the
> corrected 8 bit data, so you don't have to do much tonal correcting in PS,
> if any, unless you want to "mess-up" your image.
<snip>