I.R.I.S. Readiris Pro 12 for Windows User Guide - Manual (Page 34)

Chapter 5 – Scanning documents
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Format and Resolution
Readiris supports a wide range of paper formats and resolutions.
Note that it is recommended to use a scan resolution of 300 dpi.
Use a resolution of 400 dpi when recognizing business cards,
Asian text or very small print.
Color mode
Readiris can scan documents and open image files in color,
black-and-white and grayscale.
Contrast - Brightness
Use the slider to determine the appropriate brightness and
contrast settings, in order to obtain an optimal scan result.
Optimizing resolution for OCR
Select Optimize resolution for OCR to correct the resolution of
images scanned with too much detail (over 600 dpi). Readiris will
reduce the resolution.