[filmscanners] RE: Newish Digital Tech

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

> From: Austin Franklin
>
> Hum.  Is that true?  I don’t know that I believe that.  What, exactly, do
> you mean by noise?  Noise has MANY sources.
>
> I believe the more accurate the number of photons you capture, the more
> accurate your information.  Also, the more accurately you characterize the
> loss, as well as the more repeatable it is, the more accurate your
> information.  It also depends on the accuracy of your sensor.

Of course there are other noise sources. But light, just light electricity,
is a statistical process. At high light levels, as at high current levels,
the number of photons or electrons is so large that the random fluctuations
are a small percentage of the total. 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. (Of course, other fixed noise
sources, like electrical noise in the A/D amplifier, and quantizing noise in
the A/D converter, provide a noise floor.) Conversely, if you halve the
number of photons that you capture, the S/N degrades by 3db (as long as
that's the dominant source of noise). This is true even if you count photons
with 100% accuracy.

This explains, for instance, why my 2MP Digital Elph has lower noise in low
light than my 5MP DiMage 7. The pixels are larger, and capture more light.
The full-frame CCDs in the high-end 35mm digicams are even quieter, because
the pixels are bigger still.

> But, let’s use what you say...the Bayer pattern CCDs has only ONE
precision
> color filter over each sensor...but the Foveon has up to THREE.  One would
> reason, that by your claim, that the Bayer pattern sensors have,
> therefore, less noise.  Right?

No. In a Bayer pattern chip, each site makes use of one third of the
spectrum, and discards the other two thirds. In the Foveon chip, the other
two thirds of the light is absorbed and measured in the other two layers.
Another way of looking at it is that the Bayer pattern requires that each
pixel be divided into three separate smaller sensors, one for each color
(50% greeen, 25% red, 25% blue), and the smaller size of each sensor makes
it capture less light.

--

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


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