I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 61)

Section 6: Scanning and Opening Documents
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Color mode
Readiris can scan documents in color, black-and-white and
grayscale.
Note that grayscale and color images return the best OCR results.
Landscape
Select the Landscape option when scanning landscape-oriented
documents instead of portrait-oriented documents.
When this option is selected, Readiris displays your documents as
landscape-oriented documents in the interface.
Auto-exposure
With some scanners the Auto-exposure option is selected by
default. This option adjusts the contrast and brightness settings
automatically. A good contrast is required to obtain optimal
recognition results.
Note: when this option is selected, the Contrast and Brightness
sliders are unavailable.