1. An image processing apparatus comprising: an input device via 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 based on the calculated mean value; and an image corrector configured to apply the determined correction value to the image in order to correct the image.