Digital BW, The Print

I am glad to see that others finally got involved in the old bit depth 
discussion Austin and I have been having!
I'll address the issues below, \/

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" <
darkroom@i...> wrote:
> 
> > > If the range of the film stays fixed and the bit depth goes up the
> > > width of the raw scan shouldn't change. If you decrease the bit depth
> > > to less than the range of the film then the raw scan would get
> > > narrower?
> >
> > Martin,
> >
> > I believe this is confusing because Austin has been trying for a long time
> > to make dynamic range a function of bit depth
> 
> This is a fact. Please.  Bit depth IS a limiting factor of dynamic range in
> the way current scanners are designed.

Austin, here you are saying one thing, below you say another. Ill point 
it out later.

> > Allow me to quote Andrew Rodney (digitaldog.com):
> >
> > "Dynamic range has nothing to do with bit depth!
> 
> He is right, and I have said this too, that you can REPRESENT any dynamic
> range with two or more bits...but as I have said, that is NOT how scanners
> happen to be designed.  And for a very good reason.  CCDs output an analog
> signal that is (more or less) proportional to the light that the sensor
> elements see...and when the light is twice as strong as the another light,
> the signal has twice the strength!  AND that happens to pretty much coincide
> with "integer density ratio values".  This is just REALLY simple.
> 
> > They are completely
> > different spec1s. You can have a scanner with 16 bits per color and a
> > dynamic range of 3.3 and you can have a scanner with 12 bits and a dynamic
> > range of 3.8. Bit depth is the number of steps. Dynamic range is
> > the height
> > of the star case. You can have a staircase that1s 20 feet high and have 40
> > steps. You can have a staircase that1s 30 feet high and have 30 steps."
> 
> He is talking about theoretically, and I have stated this exact case too
> time and time again, but is had nothing to do with the reality of how
> scanners ARE designed and how they work.  A two bit scanner, though it could
> REPRESENT a dynamic range of say, 4.0, could only give you line are!  You
> would get NO tonality.

Here it is.
In this case (and many less extreme ones) how is bit depth the limiting 
factor?

All scanners used to be only 8bit, but they still captured film with 
the same d-range that the film we scan today has.  But then higher bit 
scanners came along and that allowed us to capture more tones in those 
same negatives.


> > Bit
> > depth is how many tones are used within the dynamic range, not how many
> > tones it takes to give you dynamic range.
> 
> No, that isn't how scanners are designed.  Bit depth does nothing but expand
> the tonal capture ability into the dark regions...it does NOT give more
> tones within the same dynamic range...for the same image (unless the image
> is clipping).

It does if you are talking about the old scanners vs the new. There is 
no reason to limit ourselves by saying todays scanners give us more 
than we could ever use. Film is analog, scanner makers should come out 
with a scanner that captures the full 16bits with a density range of 
todays 14bit scanners. Which would entail differentiating more tones 
rather than the ability to capture a more dense negative. I am not 
saying it is possible, but I would think someone would be able to 
figure it out. Nobody has yet because it hasn't been necessary, 10bits 
of smooth information is more than enough for any of todays output 
devices. But 16 would allow us more wiggle room for playing with the 
curves, etc...

I have taken issue with the term dynamic range. Scanner companies use 
it to mean their scanners capture more information. Which it did when 
they first started using it (comparing them to the earliest models) but 
now it only hurts the amount of information you can capture. If a 
scanner could really capture 4.5 density-range in a 12 bit space, then 
a normal negative's range would have to fit into a much smaller space 
than 12 bits. Which would mean that, with that negative, that scanner 
would actually capture less information than a 3.3 d-range, 12 bit, 
scanner.  Does this make sense?

That is one of the reasons I think they should have called it density 
range. And left the term dynamic range to something more along the 
lines of bit depth.


-mikeH
toomanyartists.com