I.R.I.S. Readiris Corporate 12 for Windows User Guide - Manual (Page 44)

Chapter 6 – Adjusting scanned documents
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o Select Smoothen color image to even out the image.
This option renders grayscale and color images more homogeneous
by smoothening out differences in intensity. As a result, a stronger
contrast is created between the foreground (text) and background
(artwork).
Note: sometimes smoothening is the only way to separate text from a
colored background.
(Original image)
(Binarized black-and-white image)
(Smoothened image)
o Select Fast Binarization to speed up the process.
When you do, the Brightness and Contrast settings will become
unavailable.
Note that selecting this option might reduce the OCR accuracy
when scanning very low-quality documents.