Scanning From The Manual Mode - Epson PERFECTION 1640 SU Reference Manual

Detect Skew Angle:
Exposure setting
The scanner automatically optimizes the exposure of an image
defined by Auto Locate. The Gamma, Highlight, and Shadow
settings are automatically set.

Scanning from the Manual Mode

2-8
Scanning Basics
The scanner automatically detects the
skew of the target image. If the document
type is photo, Detect Skew Angle applies
to each photo. If the document type is
Text/Line Art, it covers the whole area of
the image.