Image Number 7 for United States Patent #6839155.
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.