| 摘要 |
PURPOSE:To obtain a correct binary signal by obtaining a histogram of frequency in appearance on the basis of an object rated value subjected to shading correction and obtaining a branch value for binarization processing based on this histogram. CONSTITUTION:An image forming lens 4, a photoelectric converting means 5, an amplifier 6 which amplifies a detected signal, an A/d converter 7, and an operation processing device 11 are provided, and the histogram of frequency in appearance is obtained with respect to the object rated value subjected to shading correction, and the branch value for binarization is obtained based on this histogram. Even if the difference of temperature between the image part and the non-image part of the object is small, peak values of the histogram corresponding to the image part and the non-image part are specified and the bottom between both peak values is correctly specified as the branch value. Thus, the branch value for binarization is accurately specified even if the whole of the density of the image part and the non-image part of the object is shifted to a lower side or a higher side.
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