Non-contact velocity compensation system for handheld scanners
In this paper, we present a method for compensating for variations in the scanning speed of hand-held scanners that does not require physical contact between the scanning device and the scanned surface. In existing scanning devices the scanning linear array is placed parallel to the paper width (main scan direction) and moves perpendicularly to its axis (sub-scan direction). The speed with which the array moves determines the scanning resolution along the sub-scan direction. If the scanner is moved manually as in a handheld scanner the velocity with which the array moves along the sub-scan direction varies, thus causing distortions of the scanned images. In this paper, we present a system that can estimate these velocity variations using local contrast estimates. This system is unique in that it does not require contact between image source and scanning head, it can therefore be used by visually impaired users in a variety of environments. The presented velocity compensation system provides a post-compensation (apparent) velocity in the range of 1.2:1 for an initial (real) velocity variation of 10:1.
velocity compensation handheld scanners scanning devices optical character recognition