Digital BW, The Print

on 9/28/01 1:48 PM, Austin Franklin wrote:
 
>> I never knew there was a
>> justification option, and now that I do it's thrown my notion of a raw
>> scan's histogram into chaos.
> 
> It's still truly raw data either way...it's just how it's represented.
> 
>> why a piece of film with a 3.7 DR will span only a
>> portion of a
>> histogram, even IF highbit justified.
> 
> A piece of film with a 3.7 DR SHOULD span (most of) the entire histogram if
> high bit justified, and the scanner has a maximum dynamic range of 3.7
> (which would really be 3.6, or 12 bits...).

Our beloved unmentionables presumably scan at 14-bit, and reputedly capture
a DR of around 3.7, and you believe are highbit justified, yes? If I scan a
chrome and include in that scan portions which contain blown out highlights
(pure film base) and unexposed film base (frame edge) I should likely be
scanning film with a DR close to or exceeding 3.7, yes? But my data will
still span only perhaps 1/3 or 1/4 of of the histogram. What gives? It's
because it's 14 data in 16 bit space? How does that jive with the case that
the histo would be the same from a 16 bit scanner, or a 12 bit scanner. I
still don't get how the histograms should relate to each other when they are
made by different bit depth scanners.

If you could state what would occur in each of these scenarios it would be
marvelous.

1). Scan a tonally flat piece of film on a 12 bit, 14 bit and 16 bit
scanner. The DR of the film is low enough that all of these scanners can
capture the films full DR. How will their histograms compare? How will they
compare if all scanners low bit justify, and how will they compare if all
scanners high bit justify?

2). Same as above, but this piece of film has a higher DR, such that it
exceeds that of the 12 bit scanner, is exactly that of the 14 bit scanner,
and less than that of the 16 bit scanner. How do their histos look in each
of the justification instances?

I understand there probably are no 16 bit scanners, so you can either
discuss it theoretically, or just adjust all the scanners bit depths down a
notch or so.

Any other scenarios that would be useful to compare?

Ah,

3). Due to different noise levels three scanners of EQUAL bit depth have
different DR capability. A piece of film is scanned which has a DR which
exceeds one of the scanners, is exactly at that of one of the scanners, and
exceeds that of the third. Compare their histograms.

Did you eat your Wheaties today? Heck, I think I owe you a shepherd's pie
and a few pints for this. ;-)

Anyway, if you can condense this and still address the confusion that's okay
by me.

Thanks,
Todd