I.R.I.S. Readiris 14 for Mac User Guide - Manual (Page 73)

Section 6: Optimizing the Scanned Documents
68
Contrast
Move the slider to increase or decrease the contrast between the text
and the background.
Example: insufficient contrast
The image below results in broken text characters.
In this case you need to increase the contrast to obtain satisfactory
results, as in the image below.
Despeckle
Sometimes documents contain a lot of "noise" - little black spots
that occur when scanning low-quality documents or using bad
scanner settings.
To remove these little black spots, use the Despeckle slider. The
more you move it to the right, the larger the spots that will be
removed.