1. An image processing device comprising: a processor configured to execute instructions that causes the processor to provide functional portions including: a retinex-value calculating portion that calculates a retinex value of each pixel in an original image based both on a pixel value of a subject pixel and on a peripheral average luminance of the subject pixel; a normalizing-parameter reading portion that reads an upper limit and a lower limit for performing normalization; a normalizing portion that normalizes the retinex value based on the upper limit and the lower limit, thereby obtaining a normalized retinex value for each pixel in the original image; and a correcting portion that corrects the original image based both on the normalized retinex value and on the pixel value for each pixel in the original image, thereby obtaining a corrected image.