[filmscanners] RE: Newish Digital Tech

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

> From: Austin Franklin
>
> What about the sensor layers below the top one, and then below
> that?  There must be some decrease in transmission (not just due
> to the top “filter”, but due to the sensor, material whatever...).
> All the Bayer sensors measure %100 of the light that particular
> sensor is filtered for, where the Foveon gets decreased light
> to the inner two sensing areas.

The principle is that the top layer only absorbs red light, converting it to
an electrical signal, and passes the green and blue unattenuated. The second
layer absorbs the green, converting it to electricity, an passes the blue,
which is absorbed and converted by the third layer.

> Given this (and a few other issues that relate, like accuracy of
> sensing the frequency), I would speculate that the Bayer pattern
> sensor would have higher color fidelity (with respect to accuracy
> of color) than the Foveon.

If you think about how the eye works, what's important in an RGB sensor is
that each color filter have a sloped spectral response that overlaps the
adjacent color filters, and that the peaks of each response line up with the
peaks of the eye's response. This guarantees that any perfectly saturated
color of light (e.g., laser light of any visible wavelength), will produce a
different weighting of the three outputs. In the X3 chip, the skirts of the
filters are more gradual than in conventional chips, but this is something
that can be compensated for accurately using arithmetic after the fact.

> Also, this issue about “%100 of the light” keeps being stated by most
> everyone who “champions” the Foveon.  Even if it were true, it’s
> a matter of
> significance.  I do not believe it is a significant issue at all.  People
> can claim it is, but no one has yet to make any sense as to why, or shoe
> evidence of it being so.  The low light performance of the Foveon is not
> very good, in fact.  I believe if it is an issue at all, it is a
> VERY minor issue.

All other things being equal (which they're not, yet), it could prove to be
a major advantage. As I said in another post, my $350 2MP Digital Elph has
less noise than the 5MP DiMage 7 I paid $1300 for. The full frame high-end
digicams have lower noise still, all because the pixel sensors are bigger.

--

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

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