Microtek ScanMaker 3600 User Manual page 82

If your Image Type is Grayscale, only the Gray channel is
available for selection.
2. Move the black and white sliders to new points on the
histogram.
Moving the black slider
more contrast in the highlight areas of the image,
so that more detail emerges in the highlight areas.
Moving the white slider
contrast in the shadow areas of the image, so that
more detail emerges in the shadow areas.
Another alternative is to simply click the Auto button, so
that the dynamic range for the image is determined
automatically.
3. When the changes are done, click OK. For more details on the
effects of the other action buttons, see the section
Buttons.
How to use the Black/White Points
Click either one of thumbnails below to obtain a larger view.
Windows
to the right will yield
to the left will yield more
Macintosh
The Action
(Line-art image)