Method of forming halftone screen

Abstract

Abstract When converting a continuous-tone image into a halftone dot image based on halftone screen signals, a screen angle is defined as a rational tangent thereof to establish a basic periodic portion of the halftone screen signals, and the basic periodic portion is periodically generated to form a halftone screen which covers an entire scanned region of the continuous-tone image wherein the periodic portion includes a dot composed of an integral number of dot data items wherein the dot comprises four respective points defined at corners where a vertical distance 1 between an uppermost point and a leftmost point is defined by 1=L cos 2 θ tanθ where θ is the screen angle and L is a marginal edge of the basic periodic portion into which a side of the dot is projected. Minimum unit dot data items determined by the screen angle and/or a dot resolution level are prepared, and the dot data items are generated in a sequence which is established based on said screen angle and/or said dot resolution level to constitute the basic periodic portion wherein the dot data items represented by address signals X,Y are converted into dot data items represented by address signals x,y which are defined by: x=Mod(X+F(Y),Nx) y=Mod(Y,Ny) where Nx, Ny are numbers of dot data items of the basic periodic portion in the X,Y directions respectively, F(Y) is an address offset number and Mod is a modulo operator.

Inventors

• 👤 Osamu Shimazaki

Bibliographic Details