Digital BW, The Print

> Let me know if I didn't understand
> something you asked.

No, you got me great, thanks! But there are a couple of points I'm still
squiffy on. ;-)  

> It depends on calibration...but suffice to say, 0 means the scanner can't
> read anything...and 1 is really the baseline value the scanner starts
> "reading" at.  Whatever the scanner determines has a value of 1, the value
> of 2 is going to be twice as bright as 1.

Okay, this whole ratio thing: when you talk about each next value being
assigned is the next value that is read as being twice as bright as the one
before it, I think of f-stops. How can there be thousands of f-stops of
brightness in the film. Wait, I think I get it. It's a similar logarithm,
but we must be talking different units of light. The amount of light, the
size of the bucket of light which makes the first unit we call f-stop, must
be monumentally larger than the first unit of light we call  -.00015 volts?
Something like that?

>> In the instance where a manufacturer does put a high BD A/D in with a high
>> noise CCD, I get that you will still have a lot of shadow noise
>> (which again
>> are tones which have been spuriously assigned by the scanner, because it
>> can't truly distinguish them as discreet from one another, or
>> from the noise
>> of the front end?). But when you get out of that threshold area,
>> do you then
>> have more useable tones further along the scale than if you used the lower
>> BD A/D with that CCD?
> 
> That's takes a bit of an explanation.  If you have a 20 bit A/D...and a CCD
> whose noise really only give you 10 bits of good signal...you will get noise
> in all the lower bits, throughout the entire scale...but that noise that is
> between values won't really mean anything, but the noise at the end of the
> scale will be the shadow noise.  So, no, you don't get more usable tones.

If DR is the height of the staircase, and bit depth is the number of steps
to it, I would think in the above scenario that the bottom few steps
(shadow) would contain a lot of noise, but once you got past them you'd have
more steps (discrete tones) throughout the rest of the spectrum. For
instance, if an 8-bit scanner gives you 256 tones of which say the first 6
may contain noise, you have 250 discreet clean tones further up the scale.
If you have a 10-bit scanner which gives you 1024 tones, and the first 6 (or
would it be the first 24?) contain noise, won't that give you 1018 (or 1000)
discreet clean tones further up the scale? Isn't this what you were talking
about when you suggested that higher bit scans should span more of the
histogram than lowbit scans of the same material? I'm still confused about
some of those seeming contradictions, which I explained in my "from scratch"
question. Know what I'm talking about?

Getting back to dynamic range, I see how bit depth can limit DR in that it
is tied in with noise, but what else determines dynamic range? As a for
instance, if Margulis is correct, drum scanners will typically have better
DR than CCDs, even though they might both be of the same bit depth.
Furthermore, even on CCD units, what the unit's DR tests out to be may be
very different than what it's spec sheet might suggest, even when they do
list it's S/N ratio; which, granted, is probably an optimistic estimation of
it's true S/N. But my point is, I would imagine two scanners from different
manufacturers could use the same CCD and the same A/D, and yield different
DR. Is it all related to noise suppression?

Another thing I need clarification on is low-bit vs high-bit justification.

Todd