An image processing apparatus having a simple structure capable of forming high quality images. The image processing apparatus includes a document reader for generating a first luminance signal for each pixel in a color multi-valued image; a factor multiplication part for multiplying the first luminance signal by a factor to obtain a second luminance signal; a pixel-attribute determination part for determining the color attribute of a noticed pixel based on the second luminance signal; and a main controller. The main controller is configured to count an array attribute determined by an array of the color attributes for 32 lines in a block obtained by dividing a band including 64 lines in the color multi-valued image into eight in the main scanning direction, calculate image-characteristic parameters for the block based on the counted values, determine a block image attribute from the counted values and the calculated parameters, and determine the image attribute of the band based on the determination result.