An inkjet printing apparatus which performs time-divisional driving poses the following problem for at least some gray levels when halftoning control by the unit matrix is performed. More specifically, the shape of a dot cluster in each unit matrix periodically changes due to the mismatch between the unit matrix size and the unit section size of time-divisional driving. For this reason, periodical density unevenness is generated and appears as degradation of the image quality. In order to prevent degradation of the image quality, according to this invention, image data is shifted in accordance with the unit section of time-divisional driving, or the discharge timing of ink from a printhead is shifted.
