| 摘要 |
PURPOSE: To precisely detect a black frame by moving a line sensor at right angles to the travel direction of a projection image and then moving the line sensor in the travel direction of the projection image while reading a range of specific width excluding a mark for retrieval. CONSTITUTION: The scan range S0 is a scan range for a microfilm 26 when no tilt correction is made, and a scan range S1 is a scan range when an optical axis 74 is rotated anticlockwise by about 20 deg.. When a frame 26A of a document photographed on the film 26 slants anticlockwise at about 20 deg., a line sensor driving part is rotated by the same angle on the basis of a detected black frame and the scan range S0 is changed into S0 . At this time, areas nearby the corners of the original scan range S0 may be excluded from the scan range S1 . The hatched part in a rangeΔABC of the frame 26A is an unread range. The unread range becomes larger as the tilt correction quantity increases.
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