1. An image processor that corrects input image data having a predetermined grayscale range, comprising: a coefficient holding device to hold correction coefficients of a correction curve that correspond to the entire grayscale range or a portion of the grayscale range and include one or more correction points and a combination portion that is formed of a combination of a plurality of specific curve pattern portions, the one or more correction points being determined previously and independently of the input image data, and the coefficient holding device holding only the correction coefficients corresponding to one of the specific curve pattern portions in the combination portion, the held correction coefficients including a plurality of previously calculated values corresponding to a range of grayscale values of the input image data; a correction amount determination device to determine a correction amount based on statistical information of grayscale values of pixels in the input image data; and a correction device to correct the input image data by adding a product of the correction amount and the correction coefficients determined by the input image data to the input image data, the correction device including a device to generate correction coefficients corresponding to the combination portion based on the correction coefficients corresponding to the specific curve pattern portion, each of the specific curve pattern portions including a plurality of points that show a pattern of the specific curve pattern portion.