Speaking of CCD Accuracy…

[East75th <east75th@xxxxxxxxxxxxxxxx>]

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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