Method of forming halftone screen

DETAILED DESCRIPTION It is a primary object of the present invention to provide a method of forming a halftone screen to produce a better halftone dot image by eliminating a periodic pattern in the halftone dot image through the formation of dots that constitute the halftone screen with an integral number of scanning lines commensurate with the screen angle of the halftone screen.
Another object of the present invention is to provide a method of forming a halftone screen in producing a halftone dot image by superposing image information produced by scanning an original on the halftone screen composed of a plurality of scanning lines constituted by electrically generated halftone screen signals and arranged side by side in a direction normal to a scanning direction in which the scanning lines extend, the method comprising the steps of forming each of the dots of the halftone screen with an integral number of scanning lines commensurate with a screen angle of the halftone screen, and equalizing the halftone screen signals in level at mutually corresponding areas in the respective dots.
Still another object of the present invention is to provide a method of forming a halftone screen, wherein the number of scanning lines is selected so as to pass through areas of the dots where the halftone screen signals are of a maximum level.
A further object of the present invention is to provide a method of forming a halftone screen, wherein the halftone screen is composed of a repeated pattern of minimum basic periodic portions, the number .
alpha.
of scanning lines which constitute each of the basic periodic portions being selected according to the following equation: ##EQU1## where .
theta.
is the screen angle, .
gamma.
is the number of scanning lines disposed between closest vertices of a square dot with respect to the direction normal to the scanning direction, and m is an integer.
A still further object of the present invention is to provide a method of forming a halftone screen, wherein the halftone screen is composed of a repeated pattern of minimum basic periodic portions, the number