A printing apparatus which prints by scanning a printhead in two directions based on raster data containing multi-valued data, sequentially stores multi-valued data contained in each raster data in a print buffer in correspondence with a predetermined direction of the two directions, acquires for each raster data, identification information corresponding to the multi-valued data stored in the print buffer first and identification information corresponding to the multi-valued data stored in the print buffer lastly for each tone value based on initial values of identification information and the number of multi-valued data contained in each raster data, generates bitmap data from the multi-valued data using pattern data read out based on identification information selected based on a scanning direction of the printhead, and controls printing of the printhead based on the generated bitmap data.