Chuck,
> What you are saying is at least 99% wrong and I'd bet on it :-)
Name the bet.
> The CCD presents a sequence of voltage samples to the A/D, one sample per
> pixel, and the A/D makes one sample per pixel.
Correct, and I've never said anything different. But, that is only one
dimension of what a film scanner samples.
BTW, frequency doesn't have only to do with time, but can be spacial, as it
is in this case.
> Your comments about sampling frequencies are
> correspondingly incorrect
You are misunderstanding what I'm saying. A scanner is in fact sampling a
frequency. Do you understand what "MTF" is? If you do, then you clearly
would know that one of the "dimensions" that is required of a scanner to
sample IS frequency, as far as the resolution of the sensor spacing goes.
The other dimension is simply a static value, and is the tonality/intensity
of the analog signal from ONE of the CCD sensor elements at a time.
> since this is a discrete event sampling function
ONE dimension of a scanner's sampling is a "discrete event sampling
function", of course, and that is what the A/D, with only a single number,
one at a time, is measuring.
> No pixel is sampled repeatedly to reconstruct a
> frame-to-frame waveform.
In the spacial dimension, yes you are, in the tonal dimension, no, you're
not. I believe you are missing that this is a multidimensional sampling
system.
> There may
> be some difference in our topical focus that would explain why we mostly
> agree but are differing on the techie minutia that few scanner owners
would
> ever care to know about.
I stated that the number of bits of the A/D is DIRECTLY related to the CCD
output noise, and it simply is not disputable that it is. You disagreed,
and haven't shown anything showing why what I've said would be incorrect.
Even the CCD manufacturers spec their CCDs this way, saying that they are
an N bit CCD...though it's not really accurate to claim a CCD is N bits,
but that is their way of saying how many bits of clean data you can get
from the CCD.
I still don't know why you disagree with that. If you have too bits, you
don't sample all the resolution of the available signal. If you have too
many, some of the bits are simply into the noise. The correct number of
bits (which is what is at issue here), since you always have a sampling
error of 1/2 bit, is to size the A/D to equal the noise, plus one bit.
That gives you N-1 clean bits. I believe Nyquist is applicable, just in a
different dimension, and for the same reasons it applies to frequency.
Consider the noise the frequency.
> If the
> typical noise in a film's "signal"...
What is "a film's signal"? You've yet to explain how the film has a thing
to do with the number of bits for the A/D. Seriously, you ought to do some
reading on how to interface to CCDs. This is really basic stuff. I really
don't know why you are confused with this simple concept, but my guess is
that this "film's noise/signal" has something to do with it.
> ...is the approximate 1 part in 512 that HP
> lit states, then the 2x criterion would be met by a 10 bit A/D and
anything
> else (eg, 12-16 bit A/Ds) would be mismatched to the film's signal if I
> understand your language and intent. None of that makes sense.
...I believe, because you've introduced some red herring..."the film's
signal". The film doesn't have any signal. The CCD sees what it sees, and
it doesn't know what's noise and what's not, as far as what's in the image.
You don't match the A/D to anything but the CCD, which is what I initially
said, and you disagreed with...and I still don't know exactly why.
> I'm well-stocked on references and experience here.
I'm quite well stocked my self, but reference books aren't necessarily
going to give one an understanding. Have you designed a film scanner, or
any other digital imaging devices?
I'm in the US, BTW. Also, please throw that HP literature out...unless you
want to scan it and post it so I can see what on earth they are talking
about.
Regards,
Austin
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