A structure and method for improved detection of the edges of a document in
a scanner provides for positioning a width detection backer so that it is
simultaneously in the field of view of the optical element of the scanner
and out of the focal plane of the optical element. A portion of a document
is positioned in the optical path between the optical element and the
width detection backer and scanned with the optical element. Information
from the scanning step is analyzed to identify data indicative of an edge
of the document. The out of focus width detection backer, which remains
stationary while scanning the document portion presents very little
variation in intensity and other data, heightening the contrast between
the document and the width detection backer, and reducing the likelihood
of erroneously identifying elements of the width detection backer as
document edge features.
