[filmscanners] RE: Newish Digital Tech

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

> From: Austin Franklin
>
> I quote the original statement I was questioning:
>
> “If you double the number of photons
> that you capture, the random variations only increase by the
> square root of
> two, improving the signal-to-noise by 3db.”
>
> He gave no explanation of what the source for the noise was he
> was referring
> to in the original post, as far as I could tell.  You and I
> figured that one
> out as to what he must have been talking about.

I thought I made it clear that the noise I was talking about was the noise
intrinsic in the fact that the photons themselves don't arrive in nice neat
streams, but rather arrive more like the droplets sprayed from a hose.
Imagine a sensor that detects the impact of water droplets, placed out in
the rain. If the sensor is a square inch, it will produce very erratic
impulses. If it is a square foot, it will produce a much smoother stream of
impulses. If it is an acre, it will produce an almost noise-free continuous
output.

Naturally, a CCD has other sources of noise in the subsequent electronics.
But it is my understanding that in real-world digicams and scanners the
limiting factor is in the sensor itself, which is why the best digicams have
the largest pixels (thus capturing more light), and the best scanners use
photomultiplier tubes (which capture virtually all the photons, rather than
only some fraction of them).

--

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

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