Canon MultiPASS C50 Software User's Manual page 108

Under the histogram chart, you can slide the black, grey, and white
buttons to adjust the tones. However, you cannot edit the histogram
directly.
When you adjust the black-point, all tones in the image darker than the
selected black-point are adjusted to black.
When you adjust the mid-point, all tones in the image between the black-
point and the white-point are adjusted to the selected mid-point.
When you adjust the white-point, all tones in the image lighter than the
selected white-point are adjusted to white.
When you find a combination of tone settings you like, you can save the
settings in a file and use it in future scanning sessions.
To adjust the tones using the Histogram tool:
1. On the Tone tab, click the Histogram tool button.
2. To adjust the tone of a particular colour, select the colour from the
Channel list box. Otherwise, leave the Channel set to Master.
3. For the black-point, mid-point, or white-point, do one of the following
to make a change:
Click the appropriately labelled Eyedropper button. Then click the
eyedropper on the portion of the image in the preview area that is
darkest (for black-point), lightest (for white-point), or in the middle
of the tonal range (for mid-point). Try zooming in on the specific
part of the image so you can be sure you are selecting the shade
you want.
In the appropriately labelled text box, enter a tone value.
Drag the appropriate arrow at the bottom of the histogram to the
level you want.
In the preview image, all tones are adjusted accordingly.
Chapter 6 Scanning 6-25