| 摘要 |
PURPOSE:To detect noises produced by dust, flaws, etc. of a reading window by putting plural pictures read by a reading means on each other and using the signal produced by putting those pictured on each other. CONSTITUTION:An AND circuit 19 is provided together with a picture buffer 20 and a detecting part 21. The buffer 20 stores the picture information (p0, p1...p9) consisting of the same number of picture element (bits) as the picture read by the 2nd scanning part 13 and having AND secured with the signals of each picture element of the read pictures supplied successively from the circuit 19. Thus 10 sheets of postal matters p0-p9, for example, are read successively by the part 13 and only the black signals having coincident pattern signals of the postal codes are left and put on each other. Thus it is possible to detect noises produced by dust, flaws, etc. of a reading window 22 of the part 13 for said read pictures according to whether the number of black signals of the pictures (pattern signals) put on each other is equal to a prescribed level or not.
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