JPS57155541A - Formation of halftone dot for printing - Google Patents

Abstract

PURPOSE:To make edge parts sharp by forming one halftone dot of four pieces of spurious halftone dots centering respectively at the central parts on a screen line and adjacent screen lines and forming halftone dot areas from the outside end parts of the respective spurious halftone dots and the inside end parts adjacent to the centers. CONSTITUTION:In a system of converting the signals of light quantity of an original obtained with a scanner to density data and outputting the halftone dots of the areas corresponding to these density data photographically, spurious halftone dots D1-D4 are set with the central parts on a screen line inclined to 45 deg. and the screen lines adjacent thereto as centers O1-O4, and one halftone dot D is formed by the D1-D4. The point and intermediate point on the screen line corresponding to the peak positions P1 and P2 of the density data are defined as the centers O1 and O2 respectively of the spurious points T1 and DT2. With respect to the DT1, a halftone dot area DA1 is formed in the direction at a right angle to the screen line and with respect to the DT2, a halftone dot areas DA2 is formed in the direction parallel therewith, whereby the halftone dots are formed.