1. An image forming apparatus, comprising: a halftone table including different types of dot regions according to a corresponding brightness level, the dot regions comprising geometric shapes having predetermined heights and widths and non-dot regions, such that first dot regions along a line corresponding to a scan line have geometric shapes different from geometric shapes of adjacent dot regions along the line, such that the geometric shapes comprise respective sides that are each either parallel or perpendicular to the scan line, and such that the dot regions disposed in a first diagonal direction with respect to the scan line comprise lines having only the first dot regions and only the adjacent dot regions, and the dot regions disposed in a second diagonal direction normal to the first diagonal direction comprise lines having the first dot regions alternating with the adjacent dot regions; and a halftone processor to binarize an original image using the halftone table.