XIII said:
I have a Minolta Dimage E5400 scanner and Vuescan software, but am
fairly new to film scanning.
Could somebody give me a simple explanantion of what Exposure Clipping
is and under what conditions I might be advixe to change the setting
from default?
VueScan attempts to maximize the Signal to Noise ratio by increasing the
exposure time. If the exposure is too long then the data in the transparent
film areas gets clipped, i.e. many pixels will have the same maximum
brightness even if they differ in the film transparency.
VueScan tries to avoid clipping but still expose as long as possible. The
heuristic to do that is that it increases the exposure till a small (the
indicated) percentage of all pixels is clipped, and then backs up a bit
(reduces exposure time 5%).
That heuristic will usually work quite well for most images with an average
histogram shape when the default exposure clipping percentage is used. But
on predominantly dark film images that might result in overexposing whatever
little transparent areas there are. Instead of locking and reducing exposure
for each such image, you can reduce the clipping percentage. On
predominantly transparent images it is the opposite.
Bart
