Patent ID: 7301668

Claim:
A printing apparatus for forming an image on a printing medium by complementarily printing thinned-out images while scanning a printhead having a plurality of printing elements over a predetermined area on the printing medium in a main scanning direction a predetermined number of times through at least one scan in a sub-scanning direction comprising: generating means for generating a mask pattern by performing generation of patterns corresponding to the predetermined number of times in the sub-scanning direction in accordance with the number of printing elements of the printhead which corresponds to an amount by which the scan is performed once in the sub-scanning direction, and repeating the generation by the number of times corresponding to a predetermined number of columns; storage means for storing the mask pattern generated by said generating means; printing means for printing an image for each printing timing signal in the main scanning direction by using image data and the mask pattern stored in said storage means; and random number generating means for generating random numbers; wherein said generating means is capable of i) selecting a plane of a plurality of planes for generating the mask pattern on the basis of random number values generated by said random number generating means; ii) setting bit information to a target bit position of a target column of the selected plane, which target bit position is different from a target bit position of the same target column of a previously selected plane in step i); iii) repeating steps i) and ii) for the number of times corresponding to the number of lines in one column of the selected plane; and iv) executing step iii) for every column of the plane.