| 摘要 |
PURPOSE:To restrict the base fog of a regenerated image of the deterioration of sharpness of the edge part of a halftone dot image by supplying a bias current to a laser beam from a position forward of the front end of a part to be exposed of a prearranged manuscript and besides, from a position backward of the rear end of a part to be exposed of a manuscript immediately before the prearranged manuscript. CONSTITUTION:A position in which exposure begins N2 in a main scanning direction, a position in which exposure ends N3 in a main scanning direction and a position in which exposure begins M1 in a subscanning direction as well as an exposure length (M2-M1) of a part to be exposed, are read by an image processing device of an exposure control circuit 26. The image processing device subtracts a predetermined division N0 covered by the supply of a bias current 11 from the position where exposure begins N2 in the main scanning direction to calculate a bias exposure start position N1. Only the bias current I1 is supplied to a laser diode 22 in the division N0, and said diode 22 is preheated. Then, exposure is actually performed between the exposure area(N3-N) in the main scanning direction. An area to be exposed beta is exposed by the same action as for the area to be exposed alpha, and only the division N0 is exposed by the bias current I1 only once among other divisions of the part to be exposed on film F. Consequently, the deterioration value of sharpness at the edge of the parts be exposed alpha, beta is extremely low.
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