Robert DeCandido, PhD wrote:
> I have a Polaroid Sprintscan 4000 (not the Plus version) and am using
> Vuescan. When I scan a slide (either Kodachrome or Provia/35mm), the
> white areas (such as a building illuminated by the sun; or pages of an
> open book) in the scan will exhibit a "halo" effect. This appears as
> a kind of a whitish or even greenish glow surrounding the white object
> in the scan.
>
> My questions are: Is anyone else seeing this or getting this effect on
> their scans?
[Sorry if you get two copies of this. The first one was probably sent
from an address not registered and I don't think it went through]
Hi, Robert,
I have had this effect on three different units: A Nikon LS-30, a Nikon
LS-40 and a Minolta Dimage Scan Elite II. IOW, this effect seems
inherent in slide scanning and not dependent on the unit in use. I have
never seen that effect when scanning negatives, nor have I found these
halos to be real ones on the slides in question (checked under a
microscope). I have two possible explanations for that:
1. Sensor crosstalk - the brightly lit areas of the CCD may leak some of
their light into the shady areas, and there ya go. Slide film has a much
higher contrast ratio than negative film which would mean the decrease
of light intensity from bright to dark areas on a slide would exceed the
respective value for a negative by miles (10 up to 100 times), most
likely making the effect much more obvious with a slide than with a neg.
2. Film surface. Slides have a texture on their surface, following the
outlines of the subject that is on the slide. I am positive that the
thickness of the dye layers in these areas varies with this texture.
"Jumps" in dye layer thickness are likely to cause diffraction of the
light coming from the light source to the CCD, diverting light that
should "hit" the bright areas of the CCD to the dark ones. Not sure if,
and, if yes, which of those explanations apply. I haven't found anything
that would help out, apart from avoiding slides for high contrast
situations. Since I have my D60, all problems of that sort are gone
anyway ;-)
Greetings from Germany -
Ralf
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