An image processing system and method wherein image data is compressed and written to memory. The system includes a first controller, a second controller, a first detector, a third controller and a second detector. The first controller sequentially executes a reading and an image processing of image data from memory. The second controller sequentially executes a re-reading and an image processing of the image data from memory. The first detector detects insufficiency of empty capacity of the memory based on a size of image data of one page compressed at a predetermined compression rate. If insufficient memory for new image data is detected, the third controller writes new image data after a termination of the image processing of the image data of at least one page previously stored. The second detector detects overwriting by the third controller of the new image data on the stored image data.