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[filmscanners] RE: Density vs Dynamic range>AUSTIN (2a)

> From: Isidoro Orabona
> sorry, but you are confusing signals with channels capacity (see
> Shannon)!!!
> Infact you yourself cite capacity and you yourself gives a good example of
> this: the paper is the channel and the characters are the signal.

If your point is that an information carrying medium only has a "signal" on
it when the information is changing, then we're arguing about the definition
of a word. If "signal" is defined as a change in information, then I don't
see what makes a signal so much more useful than mere information. There are
lots of unchanging numeric values that represent information that is useful
to me. Indeed, in the discussion of scanners, it would seem that
"information," even if it doesn't change, is what we need to get off the
CCD, not just changing "signals."

> Make this practical experiment in your mind: get a lamp - get a photocell
> (similar to the CCD)  - amplify its output (DC offset too) -
> capacity couple
> the output - apply a oscilloscope to capacitor - aim the cell to
> lamp - now
> move your hand ahead the cell and see the trace on the oscilloscope - then
> don't tell me that the photocell isn't the CCD.

Huh? But if you don't wave your hand in front of it, you can't use it to
tell if the lamp is on or off.

Or are you arguing that scanners work by flashing the light, and measuring
the amplitude of the resulting AC signals from the CCD? I know for certain
that flatbeds don't work that way because the lamps have long time
constants. I doubt film scanners work that way, because it would involve
taking two readings for each pixel and subtracting them (either in the
analog or the digital domain) which would slow the things down by a factor
of two. But even if they did that way, that's just chopper stabilization; to
say that that little trick is what turns information into a "signal" is


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

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