A modular plastic conveyor belt constructed of flexible belt modules molded out of a material such as a flexible elastomeric compound that enables the belt to wrap closely around drive sprockets. There are prepared a transistor with a wide channel width serving as a reference, and a transistor with a narrow channel width that becomes a candidate for extraction. In the site of genetic polymorphism present in the ABO blood group genes, the frequency of heterozygote in the population is extremely high. A tone correction is performed to the original image according to the estimated black character color and the estimated ground color so as to adjust a contrast of the black character and the ground in an output image.