The present invention is an image processing method of processing an image data using an image file. The image file includes the image data and image processing control information being used for processing the image data. The method comprises the steps of: (a) determining a degree of auto adjustment for adjusting lightness and contrast of the image data according to lightness of a whole image expressed by the image data, based on the image processing control information; and (b) performing the auto adjustment based on the determination.