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Abstract

In a pre-processing system (45) for pre-processing a succession of image signals which are extracted from an object on an input surface and which are representative of a ridge pattern of the object, a center position of the ridge pattern is determined with reference to the image signal succession and is compared with a center zone of the input surface so as to decide whether or not the center position is placed at the center zone. The center position can be decided by monitoring occurrence of runs along each scanning line and by detecting a maximum one of the numbers of runs. Alternatively, the center position may be decided by monitoring ridges extended in a preselected direction with respect to the scanning lines and by detecting a maximum one of the numbers of the ridges extended in the preselected direction. The pre-processing system may detect whether the object is true or false by monitoring the image signal succession.

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First Claim