[filmscanners] RE: Newish Digital Tech

["Austin Franklin" <austin@darkroom.com>]

Hi Paul,

> > 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.

I understand that’s the ideal theory, but I highly doubt it is possible to
be %100 transmissive to the lower layers, for two reasons.  One the
absorption and second the sensing “device” that is in the light path might
block light as well.

> 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.

Possibly, but I don’t know about the repeatability across a single sensor,
as well as repeatability across sensors.  Obviously, it’s a tolerance issue.
If the range of repeatability is high enough, agreed.  I don’t have any data
to say one way or the other, that’s why it’s a question, that for me, is
unanswered.  And having designed PRNU algorithms, it sounds a lot simpler
than it actually is.

> > 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.

I don’t understand the relationship between your statement to the above
statement?  My statement had nothing to do with sensor element size, purely
the significance of sensing one color per “column” vs three.

Regards,

Austin

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