An inkjet printer includes an ink jet head having a plurality of nozzles, a head scanning mechanism moving the ink jet head in multiple passes in a scanning direction during an ink jet printing operation, and a feeding mechanism moving a print medium in a feeding direction during the ink jet printing operation. A controller determines a first time function f1(x) identifying ink ejection timing values for positions x across a width of the print medium in the scanning direction, determines a second time function f2(x) identifying ink ejection timing values for positions x across the width of the print medium in the scanning direction, and uses the first and second time functions to adjust ink ejection timing while printing on one print medium sheet.