RE: Speaking of CCD Accuracy.

["gary" <gsellani@xxxxxxxxxxxxx>]

Noise is a function of area, so you can use a larger pixel to reduce the
noise. This is one reason the astronomical CCDs are so expensive.

How do you put a neutral density filter into a film scanner? This does
sounds like a good test.

No optical system is perfect, so I could believe some light fall off at the
edges. I'm going to save the tail from the next roll of XP2 I shoot and use
it as a neutral density filter to scan.

> -----Original Message-----
> From: owner-scan@leben.com [mailto:owner-scan@leben.com]On Behalf Of
> East75th
> Sent: Tuesday, March 05, 2002 6:20 PM
> To: scan@leben.com
> Subject: Speaking of CCD Accuracy.
>
>
> I've been cursorily following the 8 vs. 16-bit thread.
>
> When one speaks of the accuracy of CCD readings does that include
> noise?  For example I did 8-bit scans on both the Nikon LS-2000
> and LS-8000
> of a neutral (gray) Wratten filter.  The standard deviations (from the
> Photoshop histogram) of this supposedly uniformly colored image was much
> greater on the LS-2000 than the LS-8000.  To me, this implies that CCD
> error extends to the whole portions of the values let alone the
> fractional.  This is just one reason for my long-standing skepticism over
> 8+-bit scanning hype.  If the whole portion of a reading is 2^0
> to 2^7 and
> the low order portion 2^-1 to 2^-8, the error for the LS-2000 is more
> likely to be + or - 2^1, perhaps even greater.  Does that sound so
> far-fetched?
>
> Also I have some other questions:
>
> 1.      Does CCD error have a normal distribution?  It seems that it must
> for multi-sampling to be effective.
> 2.      How about PMT drum scanners?  Are more accurate?  How about
> scanners such as Scitex which have cooled CCDs?  (Actually I
> should try this.)
> 3.      From what I've learned from this forum higher CCD density
> implies a
> trade-off in higher noise.  Yet clearly the LS-8000, which has a res of
> 4000 dpi, displays less noise than the LS-2000 (2700 dpi) for the scans
> that I've repeated.  What do you think Nikon has done to achieve
> higher res
> and less noise?
>
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