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


  • To: lexa@lexa.ru
  • Subject: [filmscanners] Re: Density vs Dynamic range>AUSTIN (2a)
  • From: "Isidoro Orabona" <isiora02@hotmail.com>
  • Date: Wed, 19 Jun 2002 15:26:28 +0200
  • Unsubscribe: mailto:listserver@halftone.co.uk

Hi Paul,

>Paul wrote:
>Why is this so difficult for you to grasp? The information carrying
>capacity
>of something depends upon the number of different states it _could_ have,
>not the number of states it actually attains. A page of text may have a few
>thousand characters on it, representing maybe twenty kilobits of
>information, even though there aren't 2 to the 20000 power different pages
>that actually exist in the universe. And it would have the same information
>carrying capacity even if one particular page happened to be utterly blank.

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.

>It carries information about what the voltage is, as distinguished
>from what it might be.

If a physical measurement is signal depend on the context.

>To make a scanner, you need a frequency
>response down to DC. You don't capacitively couple the output of your CCD
>into the A/D converter. It won't work. Period. Now _that's_ practical, and
>it happens to coincide exactly with the theoretical, too.

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.

Ciao,
Isidoro


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