There is disclosed an image processing apparatus which determines an attribute of an image including a pixel to be processed. An image area having a predetermined size including the pixel to be processed is extracted (S701). A variation related to the image area is calculated based on pixel values included in the image area (S705). Pixels in the image area are converted into N-ary data (ternary data or higher) in accordance with the calculated variation (S709). The attribute of the pixel to be processed is determined by analyzing the N-ary data as a result of the N-ary conversion (S711).