METHOD OF FORMING HALF TONE DOT IMAGE, METHOD OF FORMING THRESHOLD VALUE MATRIX, THRESHOLD VALUE MATRIX, METHOD OF MANUFACTURING PRINTING PLATE AND PRINTING PLATE

PROBLEM TO BE SOLVED: To upgrade print reproducibility of a half tone dot image by increasing the strength of a relief corresponding to a minimum half tone dot in the half tone dot image to be formed in a printing plate for relief-printing. SOLUTION: In the half tone dot image formed in the printing plate for relief-printing, four subclusters 68, each being composed of a single pixel, coming into contact with only the apex of a square-shape main cluster 67 consisting of 9 pixels, are radially disposed on the circumference of the main cluster 67 at the minimum half tone dot 66. Further, a projecting part corresponding to the main cluster 67 is supported by a projecting part corresponding to the subclusters 68 formed around the projecting part corresponding to the main cluster 67, at the projecting part corresponding to the minimum half tone dot 66 of the half tone dot image to be formed in the printing plate. Thus the strength of the relief corresponding to the minimum half tone dot 66, is enhanced. Consequently, the relief corresponding to the minimum half tone dot 66 is formed normally irrespective of the half tone dot area ratio of a highlight region, and in turn, the print reproducibility of the half tone dot image can be upgraded. COPYRIGHT: (C)2010,JPO&INPIT