An image processor includes a reduced image forming unit, a first reflectance value calculating unit, a normalizing parameter determining unit, a second reflectance value calculating unit, a normalizing unit, a correcting unit, and a reducing information determining unit. The reduced image forming unit reduces an original image to form a reduced image. The first reflectance value calculating unit calculates a first reflectance value for each reduced pixel. The normalizing parameter determining unit determines a normalizing parameter based on a distribution of the first reflectance values. The second reflectance value calculating unit calculates a second reflectance value for each original pixel. The normalizing unit normalizes the second reflectance values based on the normalizing parameter to obtain normalized Retinex values. The correcting unit corrects the original pixel values based on the normalized Retinex values. The reducing information determining unit determines first information based on second information with respect to at least one of quality of the corrected original image to be formed, a type of a recording medium on which the corrected original image is formed, a size of a recording medium on which the corrected original image is formed, the reduced image size, and the original image size. The reduced image forming unit reduces the original image based on the first information.