METHOD FOR MEASURING AREA RATE OF IMAGE ON PLATE IN PRINTING MACHINE

PURPOSE:To enable measurement of the area rate of an image on a plate by providing beforehand a 100% density line in some part of the plate except its image part, reading the levels of the 100% density line and the non-image part, dividing equally the levels by several tens and measuring the density. CONSTITUTION:A 100% density line 3 is beforehand provided on some part of a plate 1 except its image part 2 and while the plate 1 is held wound on a plate cylinder 4, the line 3 and the non-image part 7 are read for each of lines 61, 62, 63-6n by the sensors 51, 52, 53-5n of an area rate meter 5. The detected levels are equally divided by several tens and after the respective levels of 0-100 density levels are determined, the area rate and density of the image of the plate 1 are measured. The adjustment in the amt. of the ink to be supplied is accomplished by measuring the area rate and density of the image on the plate 1 then making calculation with an arithmetic device, applying the outputs adjusted to the openings of the blades 81, 82, 83-8n of an adjustment device for an ink fountain to the device 8 and driving and adjusting the respective blades 81, 82, 83-8n.