METHOD AND DEVICE FOR MULTI-STAGE PIXEL DENSITY SEQUENTIAL EXPOSURE OF MACHINE PLATE FOR PRINTING

摘要

PROBLEM TO BE SOLVED: To form and record images for printing which have multiple pixel density values on a machine plate for printing and to sequentially record the high-density image and low-density image at a high speed. SOLUTION: This multi-stage pixel density sequential exposing method for the machine plate for printing comprises setting image band width to narrow high-density image band width BH by a high-density exposure lens 24bH and recording the high- density image 28H by forming a narrow high-density image band 26H on the machine plate for printing while an electronic mask ML is added so that a low-density image area is shielded from a light beam in a stage wherein the high-density image 28H is formed. In a stage where the low-density image 28L is formed, on the other hand, the image band width is increased and set to low-density image band width BL so that the irradiation density of the light beam is decreased by a low-density exposure lens 24bL, and the low-density image 28L is recorded by forming a low-density image band 26L on the machine plate 4 for printing while an electronic mask MH is added so that a high-density image area is shielded from the light beam. Those high-density image forming and low-density image forming are sequentially performed in desired order for the machine plate 4 for printing to record the image 28 for printing.