I had a number of discussions with HP technical staff regarding the
banding problems in the HP film scanners, which also manifested mainly
in dark areas on slides and we batted this around a fair bit.
Banding seems to have an odd tendency to vary in making its appearance
in devices using stepper motors.
My Epson printers, for instance, seem to show banding in some levels of
density situations but not others.
I'm going to go off the deep end here and suggest a few obscure and
speculative possible explanations for why banding typically is worse in
dark areas.
With the HP I also noted the problem was most noticeable with SLIDES.
So, note that these issues relate to slides. (I know this is obvious but
with a negative, the darker areas of the film become the lighter areas
in the final image, and vice versa)
Well, firstly, it is easier to see banding in a darker area. Bright
areas have less info to see the banding with.
Secondly, perhaps brighter areas cause the CCD to bloom slightly while
darker areas do not, causing the "element" to produce a slightly larger
pixel.
Thirdly, could it be that the light areas of a slide which obviously
allow more of the light through somehow make the elements electronically
"larger" (more infra red or UV hitting them???
Finally, when the HP model was upgraded, they used a different slightly
different CCD and increased bit depth (I don't think many mechanical
changes were made) and that resulted in nearly all the banding
disappearing.
Art
I've just read another several postings ahead, and Lawrence mentioned
that changing individual profiles from each channel seems to be involved
in the banding problem he is experiencing on the Nikon ED 8000. SO, my
question is, what does profiling do to the scanner? Does it change
sensitivity or exposure time in some manner?
Since the Nikon uses unfiltered CCDs, could it be a problem with LED
flash timing versus the time the CCD circuitry is "on" for that color?
Could this be another similar problem to the jaggies where interface
timing was incorrect?
Oh, and just to make this clear... I do not own a Nikon scanner, I have
never owned a Nikon scanner, nor have I ever set eyes upon one, I
wouldn't know a Nikon scanner if one bit me, fell on my head, or broke
into my home and stole my sugar bowl. In a police line up, I could not
identify the suspected scanner, and at trial I could not point to the
Nikon scanner and say "that's the one". In fact, I am unsure if Nikon
scanners actually exist. ;-)
Tony Sleep wrote:
>
> On Wed, 18 Jul 2001 08:53:03 -0400 Lawrence Smith (lsmith@lwsphoto.com)
> wrote:
>
> > My replacement 8000 was humming right along and I thought I was home free
> > but I scanned a slide with lots of deep blue/purple sky and sure enough,
> > banding galore.
>
> Do you think this is just showing banding which is happening generally but
> hard to see, or is it just in this area?
>
> Regards
>
> Tony Sleep
> - Online portfolio & exhibit; + film scanner info
> & comparisons
