I wonder if wouldn't be useful to incorporate some 'level adjustment
widget' under xscanimage, as a complement to the custom gamma correction.
It should work very much the same very as level adjustment works under
the gimp (and probably each other image manipulation program), i.e. you
tell the program that you want the intensity range from current intensity,
say, 20 to 230 mapped to the full range of 0 to 255, because in your image
there are almost no very dark and very bright regions in the range from 0 to
19 and 231 to 255. Doing this while scanning should have the adavantage
that at least some (if not all) scanners have the ability to adjust
their absolute white and black level, so that you get always the full
range of 256 intensity shades, whereas if you adjust levels afterwards,
you lose always some shades, which sometimes makes a visible difference.
Such widget should even look very much the same as the level adjustment
widget under the gimp, i.e. you should see a histogram of the current
scan region (possibly evaluated by the preview) and you should be able
to set you new black and white levels (and perhaps the 'gamma point')
from the histogram; then the scanner gets recalibrated to the new
black and white points, and voila, you new scan is done with the new tonal
range.
Some scanner software for windows has this - in my opinion very useful,
probably more useful than custom gamma correction curves - feature. Is there
some thought of implementing something like that for xscanimage?
Steffen
renisch@fhi-berlin.mpg.de
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