[filmscanners] Re: Film resolution - was: Re: 3 year wait

["Mike Kersenbrock" <michaelk@aracnet.com>]

Austin Franklin wrote:

> I am saying that sampling at the Nyquist frequency (2f) only (reliably)
> gives you the frequency, not necessarily the amplitude (it can, if your
> point sample happens to hit the top or bottom of the wave), nor what the
> shape of the waveform was.

In terms of real implementations, I quite agree.  However in theory
(for others reading this) even when the samples hit near the zero
crossings the full height (when disregarding imperfections, noise,
etc in real implementations) will be recovered correctly.  Being
visually oriented, and liking to draw the waveforms and such, when
I took classes in this stuff 30+ years ago, I couldn't believe it.
Until I really understood what was going on (and even further emphasized
in my mind when I did a DDS (direct digital synthesis) design even
as recently as a couple years ago).  Because
I know you understand the theory, I know you know why the full amplitude
is fully recoverable in theory when running at the 2f nyquist rate (when
the rate is properly defined and in a system with ideal samplers).
Even for the near zero-crossing case.  But in
real implementations, higher than 2f will help the accuracy of things
quite bit (when measuring at the edge).

Mike K.

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