[filmscanners] RE: Pixels and Prints

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

> From: Austin Franklin
>
> Blue sky is hardly noiseless.  That doesn't mean that there can't be other
> sources of noise, some more significant than others, of course, but to
> assume that there is simply no noise in a blue sky is, IMO, a bad
> assumption.  Do you have any actual data to back up this claim?  I've
> analyzed a lot of "sky", and certainly wouldn't make a generalization like
> that.

First of all, when you look at digital images of the sky, you see some
noise; when you look at the sky, you don't. But the point is that the amount
of noise you get in the digital image depends upon the hardware, so it
obviously can't all be actual noise coming from the sky. My old DiMage 7 is
_very_ noisy, even at ISO 100. My Nikon LS-2000, scanning Kodachrome 25, or
for that matter E6 slide film, has a lot of noise, presumably from film
grain, too. My Canon 10D has much less noise in the final result.

> Of course the Bayer pattern reconciliation introduces noise, it has to by
> it's very nature.  Any time you are interpolating, you have a
> high chance of
> introducing noise.  Noise is, in this case, is introduced in both the
> spatial domain and the color domain.  No field in real life (even sky) is
> entirely "even", where all the values are exactly the same (or precisely
> linear) across a significant space.  There are many different
> interpolation
> methodologies, of course, some better than others (and I've
> designed quite a
> few), but any interpolation algorithm used for Bayer pattern
> reconciliation will introduce noise.

Noise is random, meaning that if you repeat the process, you get different
answers. If you repeat the Bayer interpolation on the same raw data, you get
the same answers. That's not noise, it's distortion. What's more, for
real-world images, with the sort of detail on which people would recognize a
loss of resolution, e.g., sharp edges, modern Bayer algorithims _correctly_
interpolate, producing what looks right to the eye.

--

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

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