Patent ID: 7751088

Claim:
A method for generating a dither matrix to print on a print medium, comprising: setting an evaluation function for calculating an evaluation value of the dither matrix; providing a dither matrix as an initial state which stores in respective elements each of a plurality of threshold values for deciding presence or absence of dot formation for each pixel according to an input tone value; fixing an element for storing a threshold value in an increasing order from a smaller threshold value while transposing at least one of the plurality of threshold values stored in a part of the elements and a threshold value stored in another part of the elements; and outputting a dither matrix in which elements for storing are fixed with regard to at least part of the plurality of threshold values, wherein the step of fixing an element for storing a threshold value comprises: transposing mutually part of the threshold values whose elements for storing have not been fixed, among the plurality of threshold values; calculating an evaluation value of the dither matrix in which the threshold values have been transposed, using the evaluation function; fixing an element for storing a smallest evaluation threshold value among the threshold values whose elements for storing have not been fixed, according to a compliance of the evaluation value to a predetermined criterion; and repeating the steps from the transposing step to the fixing step until elements for storing the at least part of the plurality of threshold values are fixed, wherein each operation of the method for generating the dither matrix is executed by a processor.