Photomechanical apparatus

Claim 1

A photomechanical apparatus suitable for use in the production of a printing plate, which is adapted to print a halftone picture corresponding to an original continuous-tone picture, on the basis of pictorial information signals obtained by photoelectrically scanning the original continuous-tone picture, comprising a tonal conversion system for converting the pictorial information signals in such a way that the base density (x) of a desired control point on the original continuous-tone picture and the halftone intensity (y) of a corresponding control point on the picture to be reproduced are correlated in accordance with the following formula ( 1): ##EQU3## where x: the base density of the desired control point on the original continuous-tone picture, namely, a value obtained by subtracting the density at the brightest area of the original continuous-tone picture from the density at the desired control point of the original continuous-tone picture; y: the halftone intensity of the corresponding control point on the picture to be reproduced; y h : a desired halftone intensity set for the brightest area of the picture to be reproduced; y s : a desired halftone intensity set for the darkest area of the picture to be reproduced; α: the reflectivity of a base material on which the halftone picture is to be reproduced; β: the surface reflectivity of a medium for visualizing the halftone picture; and k: the ratio of the density range of the halftone picture to be reproduced to the density range of the original continuous-tone picture.