Disclosed are an image processing method, an image processing apparatus, and an image processing program which perform appropriate gradation processing in each brightness region while gradation continuity is maintained. The image processing apparatus which applies image processing including gradation conversion processing to image data, the image processing apparatus having: an image processing section for applying image processing to the image data based on each of a plurality of different gradation conversion processing characteristics, thereby generating a plurality of image-processed image data; a synthesis ratio calculating section for calculating the synthesis ratios of the plurality of image-processed image data by referencing image information of the image data prior to image processing; and a synthesis section for synthesizing the plurality of image-processed image data based on the synthesis ratios, thereby generating image data to be outputted.