> Topic: "Halo" Effect
> ===============
> Date: Sat, 17 Aug 2002 06:46:47 -0400
> From: "Robert DeCandido, PhD" <rdcny@earthlink.net>
> ----------------------------------------
> Hello All,
>
> 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? Is this something gone wrong with the scanner? Is it
> something that different scan settings in Vuescan can correct?
>
> Using Knockout 2.0 I can correct most if not all of the "halo" or
> "after glow." However, if someone can set me straight regarding how
> to solve the problem before the scan, I would be most appreciative.
>
> Thanks
>
> Robert DeCandido
> NYC
>
Hi Robert,
I have observed similar "halo" effects from slides scanned with the
Sprintscan 4000. The size of the halos increase with vertical distance
from the center of the slide. The effect is best demonstrated by
example. The first image is the full image (reduced to 12.5% or 679x462
pixels, 58kb):
<>
The next image is a star near the bottom of the image (expanded to 200%
or 350x350 pixels, 43kb)
<>
The final image is a star near the top of the image (expanded to 200% or
350x350 pixels, 45kb)
<>
Notice how the red flares to the left and blue flares to the right.
Stars near the vertical center do not have flares. The effect is not
observed on similar images from negatives acquired through the same
telescope/camera combination.
Joe
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