Canon MX870 Series User Manual page 480

A printout consists of minute dots to make characters or graphs. Interfering with each dot may result
in uneven shades or a striped pattern. Select ON if you notice any uneven shades or a striped
pattern on the scanned image.
Note
Even if ON is selected for this setting, some moire effects may remain if Unsharp mask is set
to ON. In that case, select OFF for Unsharp mask.
Unsharp mask
9.
The outline of small characters or thin objects can be accentuated. Select ON if you want to
accentuate the outline of the scanned data.
* Not available when scanning a photo.
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