In the present invention, tetragons are generated, each of the tetragons being formed of four points of a point A(c, 1), a point B(a+c, b+1), a point C(0, d+1), and a point D(a, b+d+1) specified with arbitrary parameters satisfying the specified number of pixels n=2(ad+bc). From among the generated tetragons, a tetragon having an angle closest to a specified angle is selected, and two of the selected tetragons are placed adjacently to each other to generate the basic pattern. A lighting order is determined so that, continuously from a lighting order of pixels forming a first tetragon of the tetragons of the basic pattern in order of increasing distance from a specific point of the first tetragon, pixels are lit in order of decreasing distance from the specific point, and a rectangular pattern functioning as a binarization-use pattern is generated.