[filmscanners] RE: scanner dmax discussion

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> From: Chuck Cole
>
> 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.

Of course a scanner does sampling. It does spatial sampling. All the
familiar mathematical principles that apply to temporal sampling apply
equally well, albeit in two dimensions, to spatial sampling. Instead of
frequency being cycles per unit time, it's cycles per unit length, or
(fractional) cycles per pixel. You can have aliasing, which on coherent
spatial frequencies produces moire. You need bandlimiting to avoid aliasing,
which is done with an optical filter. The impulse response of the optical
filter is the shape of the blur it produces. Dither noise can increase
apparent bit depth, and break up moire. And so on.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

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