> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk]On Behalf Of
> austin@darkroom.com
> Sent: Thursday, July 17, 2003 9:46 PM
> To: cncole@earthlink.net
> Subject: [filmscanners] RE: scanner dmax discussion
>
Sorry, but I think you're out on the j omega axis if you believe that a
scanner is doing any direct implementation of a mathematical MTF algorithm
for physical optics. The scanner is in no way doing a literal sampling of
any kind of mathematical frequency function, and does not perform transforms
or inverse transforms as part of its image handling. Some computer
application software does Sobel and other image transforms on scanner data
sets, but they are not done in any of the data handling done in the scanner,
except perhaps as part of an image compression scheme AFTER an image file is
created. All my words have addressed capture and generation of the apodized
image file from the film and before formation of a possibly compressed data
file.
This has degraded to wasteful irrelevance for others and sophomoric
absurdity for us. We need a better way to agree and help each other fill
gaps in our knowledge. Let's call this one quits for now and look for a
better way or better day to continue constructive exchanges.
Regards,
Chuck
> 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?
>
Yes.. many.
> 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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