1. An image processing apparatus comprising: an acquiring device configured to acquire a typical pixel value corresponding to a noted region in an image; a calculating device configured to calculated 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; a first enhancement degree determination device configured to determine an enhancement degree according to the acquired typical pixel value and each of the calculated index values; and an image processing device configured to perform high-frequency enhancement processing on the noted region, based on the enhancement degree determined by the first enhancement degree determination device.