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Re: filmscanners: My 8000 does NOT band using Vuescan!

In a message dated 9/2/2001 8:06:37 AM EST, lsmith@lwsphoto.com writes:

> For those of you who have been following my ongoing saga with banding issues
>  with my Coolscan 8000 here is an interesting update.  I have tried the
>  latest version of vuescan and guess what?  It appears after doing a few 
>  that the banding does not occur when using that software.

I should have described what I learned about this earlier.

The LS-8000 is unique in that it has a 3-line CCD (3 lines of 10000
pixels), while all the other Nikon CoolScan scanners use a 1-line CCD.

There's a mode of the LS-8000 where all three lines are read
and then the stepper motor is moved.  This (theoretically) can
speed up scans, although not 3x because of other limitations.

However, there's one more thing to consider - all scanners
compensate for non-uniform light sources by doing a
"shading" correction.  For instance, the light intensity at
the edges of the scan is almost always at least 20% dimmer
than at the center.  In addition, each CCD element is
slightly more or less sensitive than the nearby elements.

It appears that the Nikon hardware/firmware uses the same
CCD shading for each of the 10,000 CCD positions (the
same value for 3 different pixels) instead of the more
optimal 30,000 different shading values.  This appears to
be the cause of the banding.

VueScan uses one CCD line per stepper motor position.
This still seems to be plenty fast, and there's no banding
at all when this is used (it's the only way VueScan works).

NikonScan has this same mode (I think it's called the
Fine setting) and also doesn't band when using this mode.

Ed Hamrick


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