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; 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 the product of the correction amount and the correction coefficients determined by the input image data to the input image data.