Method and apparatus for generating pseudo-halftone dots by comparing gray scale values of an original with dither threshold values stored in cells of a matrix array divided into imaginary matrices of elemental areas each containing one cell

Apparatus for generating a print signal having one of two discrete levels for each of a plurality of print positions in each of a plurality of print lines depending on a gray scale value on an original for said each print position relative to a threshold value for said each print position, comprising:

• memory means comprising an .alpha.M.times..beta.N matrix array of cells, each cell storing a unique threshold value, where M, N, .alpha. and .beta. are integers, at least one of .alpha. and .beta. being greater than unity and at least one of M and N being greater than unity, said matrix array being divided into .alpha..times..beta. imaginary matrices each containing M.times.N elemental areas, each of said areas containing .alpha..times..beta. positions and containing one of said cells at a particular one of said .alpha..times..beta. positions, said particular position being different for each of said imaginary matrices, the threshold values stored in the cells of each of said imaginary matrices having a prescribed ordered-dither distribution on the plane of said each imaginary matrix;
• first counter means for incrementing a first count for each print position in a particular print line and for addressing said memory means in a given direction in accordance with the first count;
• second counter means for incrementing a second count for each print line and for addressing said memory means in a direction normal to said given direction in accordance with the second count;
• readout means for reading out a threshold value from said memory means in accordance with the first and second counts;
• and
• comparator means for comparing the gray scale value of the original at a position corresponding to a particular print position in said particular print line with said threshold value read out of said memory means and for generating said print signal having one of said two discrete levels.