I.R.I.S. Readiris 14 for Mac User Guide - Manual (Page 71)

Section 6: Optimizing the Scanned Documents
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Example 2: text is too bright
In the image below, the text characters start to show gaps and
incomplete shapes.
To improve the recognition results:
 Check the Scanner Settings and make sure your documents
have been scanned in a resolution of 300 dpi and in color.
 If that's not the case, re-scan your documents using these
settings.
Then access the Image Adjustment options:
 Click the Adjust icon on the Image and Layout Editing toolbar.
Smoothen color or grayscale image
This option is selected by default. It smoothens out differences in
intensity, creating a greater contrast between the text and the
background. Sometimes smoothening is the only way to separate
text from a colored background.
Brightness
Move the slider to increase or decrease the brightness of your
documents.