Binarization of gray level images is a special case of segmentation with two labels [17], [18], [19] and [20]. For example, to extract characters from document images for character recognition, binarization of an input image is needed [19]. In document images, two distinct regions are defined as characters and backgrounds. Characters are objects that we desire to extract, recognize, and represent. The remaining regions are backgrounds of these objects. For most cases, digital images are obtained by a scanner or a camera. The quality of the digital images depends on image acquisition conditions such as illumination, characteristics of an input device, discriminating characteristics of objects, and so on Ref. [19].