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Abstract

An arrangement for checking or examining bank-notes or similar documents include a detector, such as a CCD array of, for example, 256 photocell devices. The documents are scanned by the photocell devices transversely of their longitudinal extent. The signals are digitized by an analogue/digital converter (2), such that the output of each photocell device is represented only by one digital bit. The analogue/digital converter (2) further defines horizontal and vertical edges of the documents and of printed images thereon, and passes the digitized signals including that of the defined edges to a position detector (6) and to a memory (4). The position detector (6) delimits the signals digitized by the analog/digital converter (2) and filtered by a filter (3) by admitting into the memory (4) for storage sixty four picture elements of selected document information with respect to vertical and horizontal outer edges as a window of 64 by 64 picture elements. A side detector (8) is coupled to and receive scanned information from the position detector (6) makes a preliminary determination as to the denomination of the document and as to which side of the document has been read. This preliminary determination is applied to the decision circuit to improve the security, of the decision based on a comparison of the window stored in the memory (4). The stored window in the memory (4) is compared, bit by bit, to reference information stored in a reference memory (5). Differences in the compared data are weighted, counted and presented to a decision circuit (13). The delimiting of information for comparison to preselected significant sections of the document based on edge detection, and a preliminary denomination and side detection in combination with comparison exhibit a high degree of security with regard to 'error decision' in the control signal.

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