| 摘要 |
Apparatus, and accompanying methods for use therein, for locating edges contained within each scan line of a scanned video image and also for locating horizontal boundaries (leading and trailing edges) of a portion of a document contained within the scan line are described herein. Specifically, this apparatus first provides a background value representative of a background level in a scanned image and associated with an incoming pixel value. If the background value exceeds a first reference value, a first signal is generated. If the incoming pixel value exceeds a second reference value, a second signal is generated. Now, an edge transition is detected based upon a pre-defined logical combination of the first and second signals. If such a transition has been detected, such as a leading or trailing edge in either the incoming pixel values or in the background level, a control circuit, illustratively implemented using a programmed array logic circuit and various counters, determines if the edge transition is associated with valid leading or trailing edge, i.e. wheter the transition itself is followed by a pre-determined number of similar pixel values. If a valid leading or trailing edge is detected, then the control circuit generates appropriate signals to store the horizontal pixel address of the incoming pixel value as a leading or trailing edge. In addition, once all the leading and trailing edes have been determined for a current scan line, then the leading/trailing edge pair having the widest spacing is selected as being the designated leading and trailing edges (horizontal boundaries) of a portion of a scanned document located within the current scan line.
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