An ink jet printing apparatus and an image processing apparatus capable of stably outputting an image with no joint streak even in the case where printing conditions, such as the kind of ink and the kind of printing medium, change in a variety of ways are provided. For this purpose, correction processing is performed on image data corresponding to an eject port group located at one end part of an eject port column in a first printing scan and on image data corresponding to an eject port group located at the other end part in a second printing scan. At this time, the number of eject ports included in a first eject port group and the number of eject ports included in a second eject port group are adjusted in accordance with printing conditions.