I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 153)

How to
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Tip 3 (Readiris Corporate only)
Make sure that favor Accuracy over Speed when processing low-
quality documents:

Click the expansion arrow on the Language group.

Move the slider to Accuracy.
Note:
When you are processing low-resolution faxes, there is no need to
take special measures. Readiris detects the typical fax resolutions
100 x 200 dpi (normal quality), 200 x 200 dpi (fine quality) and 200
x 400 dpi (superfine quality) and preprocesses these images
automatically to ensure optimal results.