>I wonder if wouldn't be useful to incorporate some 'level adjustment
>widget' under xscanimage, as a complement to the custom gamma correction.
...
>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.
For what scanners? The microtek backend already provides such
controls (and the sliders appear in xscanimage), since the
black/white levels are controllable on microtek scanners.
>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.
It's hard, I think, to incorporate the controls into the histogram,
because you don't necessarily know the true transfer function hidden
within the scanner (and thus can't really update the histogram without
doing another scan), but a histogram window alone is a neat idea.
-matt m.
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