Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1992-04-03
1993-11-16
Britton, Howard W.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358108, H04N 718, H04N 533, H04N 5217, H04N 315
Patent
active
052628523
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the domain of the permanent surveillance of a field of observation of 360.degree. or of a sector with the aid of a panoramic camera and, more precisely, it relates to a method of detection, a camera for its implementation, and a panoramic surveillance system equipped with such a camera operating in visible light or in infrared.
A panoramic camera usually delivers a signal on the basis of information supplied by integration of charges during continuous scanning of the field of observation over a sector of up to 360.degree.; the image frequency, which can be defined by the analysis time of this sector by integration of charges, differs from that of a video type signal (for example, integration time of the charges: 540 .mu.s and conventional video frame period: 64 .mu.s). Such a camera, represented diagrammatically in FIG. 1, is composed mainly: space analyzed onto a photodetector module; photodetector cells associated respectively with p stages, E.sub.1 to E.sub.p, of a read shift register R delivering a signal at the level of an output 5 through an amplifier A; array b and associated with an analysis circuit 4 of the speed of rotation of the array so as to transfer the charges synchronization with the rotation of the array b; of a support having a vertical axis, for example a tower 7, on which the optical system/photodetector assembly is installed.
The operation of such a camera is conditioned by the values of duration parameters. The duration separating two successive analyses of the same part of a space is given by the period of rotation T.sub.r. It has to be short, of the order of a second, in order to permit rapid detection of objects appearing in this space. In the course of one complete rotation, the photodetector array b is periodically taken into integration of charges during an integration time T.sub.i. In the course of this period, the quantity of charges integrated in the silicon substrate facing each cell is proportional to the quantity of photons received. At the end of each integration cycle, the integrated charges are transferred into a read register R. The synchronization clock circuit supplies charge transfer control signals from stage to stage up to the output 5. The electrical signal thus obtained at the output 5 is representative of the variations in luminance from top to bottom of the angular sector of the field of observation analyzed. The width of the sector analyzed depends on the number of readings per complete rotation, and thus ultimately on T.sub.i.
The assessment of the performance characteristics of a panoramic camera results from the assessment of various criteria, in particular: corresponding to a given variation in luminance;
More precisely, the performance characteristics of this type of camera are linked to the values of T.sub.i and to the T.sub.i /T.sub.r ratio: time, is good but the sensitivity diminishes since fewer charges have been able to be integrated;
Optimization of this system leads to shortening the time T.sub.i while increasing the sensitivity to the maximum with the aid of a high electronic gain. But these conditions of use bring about a poor signal
oise ratio, that is to say poor discrimination between target detection and detection of a temporary noise peak due to the high gain, this poor discrimination being able to lead to a false alarm. In order to remove the uncertainty, it is necessary to wait for the next pass or passes of the detection system in the same direction (i.e. one or several times T.sub.r), which can be extremely detrimental to rapid targets taking account of the speed of rotation of the tower.
Moreover, the mounting of a panoramic camera on a mobile craft (terrestrial, aerial or marine) entails faults in the image due to the movements of the vehicle, these faults being capable of being amplified by errors in the speed of rotation of the axis of the camera.
The object of the invention is to overcome these drawbacks by proposing a method of detection and a camera for its implementation intended to: time T.sub
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Eouzan Jean-Yves
Heurteaux Jean-Claude
"Thomson-CSF"
Britton Howard W.
LandOfFree
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