Abstract

A halftone signal having one of two discrete levels is generated for each print position along each print line by comparison between a gray scale value of an original with a threshold value stored in a memory. The memory has an ଱M×ଲN matrix array of cells each storing a particular threshold value, where M, N, ଱ and ଲ are integers. The memory is divided into ଱×ଲ identical imaginary matrices of M×N elemental areas each containing a cell in a particular one of ଱×ଲ positions. The threshold values stored in each imaginary matrix have a prescribed ordered-dither distribution and those stored in positionally corresponding elemental areas have a dot-dispersive or a dot-concentrative distribution. The memory is addressed in a given direction in response to each print position and in a direction normal to the given direction in response to each print line to read a stored threshold value for each print position for comparison with the gray scale value.