| 摘要 |
PURPOSE:To decide a space sandwiched with a differential value over +Th and a differential value less than -Th as an irradiation field. by finding a difference between adjacent picture data from read picture information, and comparing the differential picture with a prescribed threshold value Th. CONSTITUTION:The picture information accumulated and recorded on a cumulative phosphor sheet 10 by pre-reading from the sheet 10 is read. At this time, when photography is performed by applying rectangular irradiation field diaphragm, the levels of picture data in the irradiation field 12 and the irradiation field 14 are different, therefore, pulsewise signals at a part where it changes from out of the irradiation field to the irradiation field, and a part where it changes from the irradiation field to the out of the irradiation field as shown in figure can be obtained. Therefore, the prescribed threshold value Th is set, and by comparing the differential picture data with the threshold value Th, the differential value over the +Th (point where it changes from the out of the irradiation field to the irradiation field), and the differential value less than the -Th (point where it changes from the irradiation field to the out of the irradiation field) are decided, and the part sandwiched with those tow points is decided as the irradiation field in a direction of an X-axis.
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