| 摘要 |
PROBLEM TO BE SOLVED: To change the threshold in response to the peripheral condition so as to more quickly and securely decide the generation of X-rays radiation in an image forming device. SOLUTION: In an image forming device to be used for especially in a field of dentistry, a solid state image forming device 3 is continuously clocked out during the waiting time before the radiation from an X-ray source. The signal drawn from a CCD 3 is compared with a threshold in a compactor 7 so as to decide the generation of radiation form the X-ray source 1 as a quick change in the signal level. The threshold condition is changed so as to follow a change of the peripheral condition, especially, temperature change, and an increase of the dark current with a rise of the temperature is allowed. the threshold for triggering the CCD so as to start the catch of the image is set at a relatively low level, and the risk of the wrong trigger operation can be restricted at the minimum.
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