It aims to prevent occurrence of gradation jump or color displacement even if a process for improving a brightness distribution of a digital image to be processed is performed. An image processing method for achieving such prevention comprises: an extraction step of extracting a brightness component from image data; a scale conversion step of obtaining a distribution of the brightness component on relatively large scale; an improvement step of improving the brightness component distribution of the image data by using the brightness component and an output in the scale conversion step; and a gradation compression step of judging whether or not the image data reconstituted according to the improved brightness component distribution is within a predetermined color gamut, and, when it is judged that the reconstituted image data includes the image data outside the predetermined color gamut, of performing a gradation compression process.