device to eliminate the influence of background radiation on the image reproduction in a infrared camera

摘要

1436801 Infra-red camera AGA AB 13 Feb 1974 [6 March 1973] 06479/74 Heading H4F In an infra-red camera in which the video signal from an infra-red detector 4 is A.C. coupled (capacitor 10) to a display CRT 14, to prevent that portion of the video signal which represents undesired information from the camera housing picked-up between each sweep of the scanning element 3 influencing the meanvalue of the A.C. video voltage, the video signal is blocked by FET 8 in response to timed control signals generated in logic unit 13 in synchronism with the scanning element movement. Thus the mean value (grey tone) in the displayed image is determined only by the A.C. voltage part of the video signal which contains the desired image information, i.e. the voltage over capacitor 10 is the same during time T 1 -T 2 as it was at time T 1 -see Figs. 2b and 2c. The D.C. voltage level of the video signal may be adjusted 15, 16. The scanning element may comprise one or more rotating silicon prisms, mirrors or mirror drums. In a conventional D.C. coupled camera, switch 11 is closed and grey-tone balancing is effected 5, 6, in dependence upon the absolute temperature of the object scanned.