| 摘要 |
PROBLEM TO BE SOLVED: To enable a proper binarization by performing specified calculation for calculating a threshold value on the basis of physical quantity regarding noises occurring at an edge detection process image. SOLUTION: The upper limit value and the lower limit value within a range of brightness level where noise is generated are set. Then, an average value Navg in the range is obtained. Then, as in the equation, for example, Th= kμNavg, the noise average value Navg is multiplied with a specified factor k, so that a threshold value Th which is larger than noise level and smaller than edge level is calculated. Factor, equation, and noise's upper limit/lower limit values are determined experimentally in advance. By binarizing with thus obtained threshold value, only edge can be detected.
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