Optical printer

A color printing method in which the surface of a sensitized sheet is divided into a plurality of regions (1, 2, 3 . . . N . . . ) in the scanning direction of an optical head and gradations for first, second, and third colors are assigned for each region by image data, comprising steps of:

• (a) opening a shutter of the optical head, radiating a light beam of a first color with a given width toward an N-th region on the sensitized sheet, then moving the optical head to move the light beam in the scanning direction of the optical head, and closing the shutter in a position reached by the light beam advanced from a radiation start position by a distance d11 (≦D) assigned by the image data;
• (b) opening said shutter again after moving the optical head by a distance which allows the light beam of the first color to move for a preset distance D, radiating a light beam of a second color with the width W toward an (N−1)-th region on the sensitized sheet, then moving the optical head to move the light beam in the scanning direction of the optical head, and closing the shutter in a position reached by the light beam advanced from the radiation start position by a distance d12 (≦D) assigned by the image data;
• (c) opening said shutter again after moving the optical head by a distance which allows the light beam of the second color to move by the preset distance D, radiating a light beam of a third color with the width W toward an (N−2)-th region on the sensitized sheet, then moving the optical head to move the light beam in the scanning direction of the optical head, and closing the shutter in a position reached by the light beam advanced from the radiation start position by a distance d13 (≦D) assigned by the image data;
• (d) opening said shutter again after moving the optical head by a distance which allows the third color light to move by the preset distance D, radiating the light beam of the third color with the width W toward an (N+1)-th region on the sensitized sheet, then moving the optical head to move the light beam in the scanning direction of the optical head, and closing the shutter in a position reached by the light beam advanced from the radiation start position by a distance d21 (≦D) assigned by the image data;
• and
• (e) executing the same operation thereafter.

An optical printer apparatus comprising:

• an optical head radiating a plurality of color light beams while moving relatively to a sensitized material, and
• a drive unit for driving at least one of the optical head and the sensitized material in order to cause the optical head and the sensitized material to move relatively to each other at constant speed, wherein
• said color light beams are radiated one by one on a time-sharing basis without simultaneous radiation among them, and in a predetermined order periodically in association with the relative movement of said optical head with respect to said sensitized material, and
• an image width W of said color light beams on the sensitized material in the direction of said relative movement is smaller than a maximum exposure distance D which is the relative movement distance of said optical head with respect to said sensitized material, and which corresponds to a maximum exposure time of said color light beams.