According to an embodiment of this invention, an image processing apparatus generates image data to be used to print an image on a print medium, based on a print job transmitted from a host, generates first print data by performing image processing on part of the generated image data, stores the first print data in a first memory, generates second print data by performing image processing on a remaining part of the generated image data, and stores the second print data in a second memory. The apparatus further transfers the first print data from the first memory to the second memory, composes the first print data and the second print data stored in the second memory, and transfers the composite data as print data to a continuous area of a third memory.