> 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
Does the halo only appear along one direction, or evenly in all
directions around the highlight? Since film scanners only use one CCD
line, this leaking can obviously only take place in on direction.
> 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
The thickness has no more effect that the density variations. As long
as the texture is thinner than the features of the picture (which is
the case), it has no influence on diffraction.
> 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
Then, however, you should also see a halo under the microscope or with
a (condenser) enlarger, or even with a slide a projector.
I think the problem is flare within the scanner. In the case of the
Nikons at least, I'm sure it is caused by dust, because their optics
are damn good.
Andras
===========================================================================
Major Andras
e-mail: andras@users.sourceforge.net
www:
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