There is provided an image processing apparatus which can effectively use a memory provided in an image pickup apparatus such as a digital camera or a digital video camera, without causing a shortage of the working memory capacity during image processing of print data, to realize a printing system that has minimized costs and is very flexible. Image data stored in a recording medium is input to the image processing apparatus. An image data format for conversion of the image data is selected according to a size in which the input image data is to be printed out and the input image data is processed in the selected image data format.