I.R.I.S. Cardiris 4 - Manual (Page 66)

Chapter 7 – Reference Information
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Note that this is not the standard scanning resolution of a Twain
scanner.
Calibrate
Insert the calibration sheet and click the Calibrate button to
calibrate the scanner.
Format
You can either choose an automatic or custom scanning format, or
you can opt for the Business Card format in which the scanning
dimensions are set to 8.89 cm x 5.08 cm.
When you're using the I.R.I.S. Business card scanners IRISCard
Pro 4 or IRISCard Mini it is recommended to use the automatic
format. Cardiris applies autocropping to reduce the scanned surface
to the calling card. White space around the business card is erased
automatically to obtain the smallest possible images that are
optimally legible.
Select the custom format when you're scanning prescanned images.
Automatic deskewing will not apply here.
Color Mode
Cardiris supports black-and-white, grayscale and color images.
Scan settings of the IRISCard Pro 4 and IRISCard Mini
 Select a scanning resolution of 400 dpi
.