I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 77)

Readiris TM 14 – User Guide
83
In this case you need to darken the image to obtain
satisfactory results.
Contrast
Move the slider to increase or decrease the contrast between the text
and the background.
Example
The image below results in broken text characters.
In this case you need to increase the contrast to obtain
satisfactory results.
Despeckle
Sometimes documents contain a lot of "noise" - little black spots
that occur when scanning low-quality documents or using bad
scanner settings.