| 摘要 |
PROBLEM TO BE SOLVED: To provide a picture sensor which can surely discriminate between a trespasser and the background without increasing the quantity of infrared light thrown to an area to be monitored. SOLUTION: A picture 2 obtained by photographing the area to be monitored while throwing infrared rays different in wavelength (810 nm and 950 nm) to the area and a picture 1 obtained by photographing the area at the time of normalcy are compared with each other by a discrimination means, and it is judged based on a differential picture 3 whether the state of the monitor area is normal or not. Since the background and a trespasser in the monitor area have different reflection factors by wavelengths of thrown light, reflection factors of the background and the trespasser are different in at least one picture, and they are easily discriminated in the picture. Thus, it is unnecessary to increase the quantity of infrared light to be thrown.
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