1. A visual processing device comprising: an image partitioning unit operable to partition an input image into a plurality of image regions; a region gradation transformation property derivation unit operable to: derive a target-image-region gradation transformation property for a target image region of the plurality of image regions, according to a characteristic value of a wide image area surrounding the target image region; and derive at least one adjacent-image-region gradation transformation property for at least one adjacent image region that is adjacent to the target image region, according to a characteristic value of a wide image area surrounding the at least one adjacent image region; and gradation processing unit operable to perform gradation processing to produce a transformed value of a target pixel of the target image region, based on (i) a value of the target pixel, (ii) the derived target-image-region gradation transformation property, (iii) the derived at least one adjacent-image-region gradation transformation property, and (iv) a position of the target pixel, wherein the gradation processing unit performs the gradation processing, such that when the value of the target pixel is a predetermined value, the transformed value of the target pixel monotonically decreases with respect to an average value of pixels included in the wide image area surrounding the target image region.