Disclosed herein are an image processing apparatus, an image capturing apparatus, an image processing method, and a method of controlling an image capturing apparatus. The image processing apparatus includes: an input unit through which an image is input, a correction value decider configured to detect an edge of the image by applying at least one directional filter that is alignable in a direction with respect to the image, to calculate a mean value of a plurality of pixel values of a plurality of pixels that correspond to the edge, and to determine a correction value that corresponds to each pixel of the image according to the mean value of the plurality of pixel values, and an image corrector configured to apply the correction value to the image in order to correct the image.