1. An image processor comprising: a reduced image forming unit that forms a reduced image by reducing an original image; a reduced image peripheral average value generating unit that generates a peripheral average value for each pixel of the reduced image by performing a filtering operation on a peripheral pixel region for the each pixel, the peripheral pixel region including peripheral pixels for the each pixel, the peripheral pixels for the each pixel including the each pixel and pixels adjacent to and surrounding the each pixel; a reduced image reflectance component calculating unit that calculates a reflectance component indicating a ratio of brightness between each pixel and the peripheral pixels thereof for the each pixel in the reduced image based on the results of logarithmic operations performed on the peripheral average value and the value of the each pixel in the reduced image; a frequency distribution generating unit that generates a frequency distribution of the frequency of each value of reflectance component calculated by the reduced image reflectance component calculating unit; a representative reflectance component determining unit that determines a representative reflectance component based on the frequency distribution; a normal correcting unit that performs a normal correcting operation for correcting a value of a target pixel in the original image, the normal correcting unit including: an original image peripheral average value generating unit that generates a peripheral average value for the target pixel of the original image by performing a filtering operation on a peripheral pixel region for the target pixel, the peripheral pixel region including peripheral pixels for the target pixel, the peripheral pixels for the target pixel including the target pixel and pixels adjacent to and surrounding the target pixel; an original image reflectance component calculating unit that calculates a reflectance component indicating a ratio of brightness between the target pixel and the peripheral pixels thereof in the original image based on the results of logarithmic operations performed on the peripheral average value and the value of the target pixel in the original image; and a converting unit that converts the value of the target pixel in the original image to an output value based on the reflectance component of the target pixel and the value of the target pixel, thereby calibrating the value of the target pixel in the original image according to the ratio of brightness values between the target pixel and the peripheral pixels thereof; and a simplified correcting unit that performs a simplified correcting operation for correcting the value of the target pixel in the original image by converting the value of the target pixel to an output value based on the representative reflectance component and the value of the target pixel in the original image.