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filmscanners: Noise (was: Printing A3 from a 2700dpi scan



It appears to me that Rob is talking about "grain-aliasing" (in negs), and
Joe is talking about "noise" (in the blue channel). To me the "noise"
phenomenon looks almost identical to aliasing in either slides or negs, and
yes, it's predominant in the (dark) blue channel in both cases. It always
appears in the same scenario--dark blue subject matter and/or shadow detail
in bright sun, which adds the matter of "dynamic range" to the equation.

I'm less interested in the "why's" of the problem than in a means of dealing
with it. After all, what's done is done, and getting acceptible
results--short of retouching a picture pixel-by-pixel--is the next
consideration.

Best regards--LRA


Joe wrote:
> CCD's (Charged Couple Device) used in scanners and digital cameras
> are least sensitive to blues, making it difficult for them to
> interpret those colors correctly. File compression (such as with
> jpeg) can also contribute to noise in the blue channel.

Rob wrote:
>OK, but as I mentioned earlier - we're talking about *negatives*
where this problem is most evident, not transparencies, so the
colour the CCD sees isn't blue at all.


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