1. An image processing apparatus comprising a central processing unit programmed to: acquire a typical pixel value corresponding to a noted region in an image; calculate index values of variances in pixel values in the noted region or in both the noted region and a region adjacent to the noted region; determine an enhancement degree according to the acquired typical pixel value and each of the calculated index values, wherein the enhancement degree is determined based on a first relation between each of the index values and the enhancement degree, wherein possible values for the typical pixel value are divided into a plurality of ranges based on sections of a subject, and wherein the first relation is different for each of the plurality of ranges such that a first relation for a first range of the plurality of ranges applied to an index value is different from a first relation for a second range of the plurality of ranges that would be applied to the same index value; and perform high-frequency enhancement processing on the noted region, based on the determined enhancement degree.