Patent ID: 8418612

Claim:
A printing plate making apparatus configured to scan a recording medium by a light beam at a predetermined pixel pitch, thereby engraving a surface of the recording medium to make a printing plate, wherein: the light beam includes a first light beam and a second light beam, a light power of the first light beam is P 1 , a light power of the second light beam is P 2 , and depths engraved by the respective light powers are d 1 and d 2 ; the printing plate making apparatus is configured such that, after scanning the recording medium with one of the first and second light beams at a predetermined pixel pitch to engrave the recording medium to a first depth d 1 or d 2 , a scanning line scanned by the one light beam is scanned by the other of the first and second light beams and the recording medium is engraved to a second depth d 1 +d 2 which is deeper than the first depth; an upstream end of a convex portion forming an upper portion of a region where the recording medium is to be left in a convex shape is defined as an upstream reference position; the printing plate making apparatus is configured to control light power of the first light beam such that, when the recording medium is scanned at a predetermined pixel pitch with the first light beam, from a first point which is separated from the upstream reference position by m pixels in the scanning direction, or the vicinity thereof, to a second point on the surface of the recording medium separated from the upstream reference position by n pixels downstream in the scanning direction, a light power of the first light beam is reduced linearly or substantially linearly from P 1 such that at the upstream reference position or the vicinity thereof the light power of the first light beam is equal to or less than a threshold engraving energy; and when the recording medium is scanned by the second light beam at a predetermined pixel pitch, from a third point or the vicinity thereof, the third point being separated from the upstream reference position by (2m+n)×(P 2 /P 1 ) pixels in the scanning direction, the printing plate making apparatus is configured to reduce the light power of the second light beam linearly or substantially linearly from P 2 such that it becomes the threshold engraving energy or less at the first point or the vicinity thereof.