There is provided an ink jet printing apparatus capable of printing an image having few joining stripes. Dot count is performed regarding an image printed in the vicinity of the joining stripe, and print duty is judged. Next, a dot count value is determined from the print duty. Then, a print data correction rank is determined beforehand in accordance with properties of the printing apparatus, and image data to be printed in the vicinity of the joining stripe is added or thinned out. Thus, an image can be printed which has few black and white stripes.