| 摘要 |
PURPOSE:To always exactly adjust the focus to the surface of an original picture by deriving an aggregation excluding a contrast signal which has been separated greatly by the reverse side of the original picture of every area, determining the contrast signal in a position of a projection lens, and deriving a lens position where the contrast signal becomes maximum. CONSTITUTION:A CPU 78 reads contrast signals C1-C4 through an A/D converter 74 and an input interface 76 in accordance with proceeding of a scan. The CPU 78 derives an aggregation consisting of C1, C2 and C4, in which they are adjacent to each other, and also, many contrast signals are contained, from among the contrast signals C1-C4, sets their arithmetic average (C1+C2+C4)/3, as a contrast signal (x) in this lens position (x), and stores it in a RAM 82. The CPU 78 moves a projection lens 20 by a prescribed quantity and executes repeatedly its operation, and derives a lens position xF where the contrast signal becomes maximum. In this way, even if dust or a flaw exists on the reverse side of an original picture, the focus can always be adjusted exactly to the surface of the original drawing. |
