Printing apparatus and driving method therefor

A printing apparatus including an inkjet printhead with not less than two nozzle arrays arranged in a first direction, each nozzle array including a plurality of nozzles arranged along a second direction intersecting the first direction, the apparatus comprising:

• a conveying unit configured to convey a longitudinally long-shaped sheet in the first direction;
• a driving unit configured to drive the printhead so that each nozzle performs preliminary discharge on the sheet conveyed by the conveying unit while printing a dot based on print data;
• and
• a unit,
• wherein the unit performs
• a first operation of expanding image data onto a memory in correspondence with the first direction and the second direction,
• a second operation of, in each nozzle array for every column data corresponding to the second direction in the expanded image data, selecting some of the plurality of nozzles as non-driving nozzles so the nozzles do not overlap each other between the nozzle arrays in the first direction, and the remaining nozzles of the plurality of nozzles as driving nozzles,
• a third operation of determining, for the expanded image data, image data to be assigned to each nozzle array so that when a portion of each column data indicating driving of a nozzle corresponds to a driving nozzle selected for the column data, the portion indicating driving is assigned to a nozzle array to which the driving nozzle belongs, and when a portion of each column data indicating driving of a nozzle corresponds to a non-driving nozzle selected for the column data, the portion indicating driving is assigned to another nozzle array different from a nozzle array to which the non-driving nozzle belongs,
• a fourth operation of generating data for preliminary discharge which corresponds to the image data determined in the third operation and is used by the plurality of nozzles of each nozzle array to discretely perform preliminary discharge on the sheet in at least one of the first direction and the second direction, by setting, when the nozzle selected as the driving nozzle in the second operation for given column data is set as a preliminary discharge target, the column data as data used by the nozzle to perform preliminary discharge, and setting, when the nozzle selected as the non-driving nozzle in the second operation for given column data is set as a preliminary discharge target, another column data, which is different from the column data and in which the nozzle is selected as the driving nozzle in the second operation, as data used by the nozzle to perform preliminary discharge, and
• a fifth operation of generating print data by ORing the image data determined in the third operation and the data for preliminary discharge generated in the fourth operation, and outputting the print data to each nozzle array.