A METHOD OF SIGNAL PROCESSING OF OPTICAL SIGNALS

Abstract: A signal processing device to receive signals from an optical detector (1) and comprising a first profile integrator (4) and a second profile integrator (7) each having different time constants, and a comparator arranged to receive the signals from the integrators (4-7) to detect and indicate change in the two signals at a selected time.

Description: "A METHOD OF SIGNAL PROCESSING OF OPTICAL SIGNALS" This invention relates to a method of signal processing which can be used in visual or infrared intrusion alarms or similar systems. Infrared and visual scenes are generally so cluttered as to render the detection of targets such as intruders or vehicles, 5. extremely difficult. Various forms of movement detectors related to video images are already known and as an example the specification of PCT Application Nb. W082/01454 by The Ccrrmonwsalth of Australia refers to such a systαn where areas are scanned and movement in such areas 10. is recorded, the s-c-annings in that case being related to windows which can be selected to limit the clutter which could occur f om adjacent zones. The object of the present invention is to provide a msthod of and means for detecting change or irovement in a simple effective 15. manner. A feature of this approach is to adapt to both spatial and taπporal changes in the background clutter. The method ccπprises a simple processing technique of ironitoring the background signals and the detection of any small changes to 20. them. The invention consists in the processing of an optical signal which can be visual or infrared to provide two channels, the one channel having a higher decay rate than the other, and the indication of change or movement is obtained from the difference in output 25. between these two channels. The invention can be readily carried into effect by using an optical scanning device which produces a t_Lme-va__ying signal representing the spatial variations of radiance in the scene. This signal is amplified .and passed through two profile integrating 5. stages, the first of short term duration to provide signal to noise enhancement whilst πaintaining a fast response time, the second of long term representing the averaged scanned scene over the long term. When these two signals are compared, the difference indicates a change or movement in any part of the scanned scene. 10. In order that the invention will be fully appreciated an embodiment thereof will be described with reference to the ac<_x_crιpanying drawing which is to be taken as illustrative only and not as limiting the invention. In the drawings:- 15. FIG. 1 is a block diagram depicting the invention, and FIG. 2 is a compound graph showing sequentially at A the output frαn a first profile integrator, at B the output frcm a second profile integrator and at C the output from a difference amplifier. 20. It will be realised that the output can be the signal from a single detector, or multiple detector signals can be cxmbined and processed. For a single detector, scanning is achieved opto-mechanically, as for example, achieved by a rotating reflecting polygon or 25. v_Lbrat_ing mirror. For a detector array, scanning is achieved by multipl-exing the array output. The signals frαn the detector 1 are fed to an A.C. coupled discrete low-noise, high gain preamplifier 2, then through a band-pass filter 3 centred on the scan frequency with a Q of 3. The scan 30. frequency is typically 100 Hz. This signal is then passed through an initial stage of analogue integration in the first profile integrator 4. This consists of an amplifying stage 5 with a CCD analogue delay line 6 in a positive feedback configuration. The delay line is 5. synchronised with the scan frequ-sncy. The -complete scan cycle is integrated, the time constant of which is in the order.of 4 cycles. This stage is used to enhance the signal to noise ratio as generated by the detector (short term store) . The enhanced signal is then fed to a second profile 10. integrator 7 which comprises a sync_hronous integrating stage consisting of an amplifier 8 and associated analogue delay line 9 in a feedback path. Here the time constant is made much longer, in the order of one second (100 cycles) . This stage functions as a long- term store. 15. The outputs of the first and second profile integrators 5 and 7 are then ccrtpared in a comparator 10. With a steady-state scanned profile no output is generated by the comparator. When a change of .scene occurs due to a moving body wάthin the field of view, the input signal is sensed to differ from the profile as 20. stored in the long term store. The resultant output signal fr n the comparator has a large ccπponent synchronous with the scan frequency. A p3__3se-locked tone detector 11 is used to detect output at this frequency and an alarm is triggered when a threshold level is exceeded. 25. The advantages of this technique lie in the high s-ensitivity, high clutter rejection, real time operation and low power consumption using low cost analogue hardware. As defined earlier, the output frαn the first integrator 4 as shown at A in FIG. 2 has an envelope different than the envelope 30. generated by the second stage integrator 7 as shown at B in FIG. 2 and this difference results in a signal as shown at C in FIG. 2, indicating a change in the data received by the detector 1. The first profile integrator 4 and the second profile integrator 7 are connected to a phase locked loop generator 12. In operation as the target enters, the first profile integrator responds rapidly as shown in A in FIG. 2. The 5. middle trace B shows the slower response of the second profile integrator. These two signals are compared in the difference amplifier. Here, the signal initially rises with the faster response of the first integration loop, then once again falls away as the longer term second profile integrator responds to 10. the change. A similar perturbation will occur when a target moves frcm the field of view. Alarm is initiat-sd the output frαn the difference amplifier exceeds a set threshold.

Claims: THE CLAIMS DEFINING THE INVENTICN ARE AS FOLLCWS: 1. The method of signal processing of optical signals in which an area is scanned for change detection by visual or infrared beam, in which the said scanning beam is processed to detect changes in the image, characterised by dividing the 5. signal into two channels, causing one channel to have a higher decay rate than the other, and comparing the two channels after an elapsed time to indicate change. 2. The method of processing optical signals according to Claim 1 to detect a change in such signal as brightness or motion in which an optical, signal from a scanning system is fed to a detector and the output of the detector is processed to detect 5. change, characterised by the steps of; submitting the signal from the detector (1) to a first profile integrator (4) , integrating the scan cycle to enhance the signal, feeding the enhanced signal to a second profile integrator (7) having a longer time 10. constant than the said first integrator (4) , su___nitting the outputs of the first profile integrator (4) and the second integrator store (7) to a comparator (10) and using the differential between the said signals in the comparator (10) to generate an output signal. 3. The method of Claim 2 wherein the signal frαn the said optical detector (1) is passed through a low noise preaπplifier (2) and a bandpass filter (3) , and the signal frαn the •comparator (10) is.submitted to a tone detector to generate said 5. output signal. .4. The method of Claim 2 or 3 wherein the said first profile integrator (4) and the said second signal integrator (7) are connected to a clock generator (12) receiving a scanning signal frαn the said scanning optics. 5. A signal processing device for processing optical signals to detect a change in such signal as brightness or motion in which a scanner directs the said signal to an optical detector (1) characterised by a first profile integrator (4) and a second profile 5. integrator (7) arranged to receive the signal from the said detector (1) , means to have different time constants in the said first and second integrators (4-7) , a comparator arranged to receive the signals from the said first and the said second integrators (4-7) to detect change in the signals from the said 10. first comparator (4) and the said second comparator (7) and means to indicate such change. 6. A signal processing device according to Claim 5 characterise by means to enhance the said signal in said first integrator (4) , and tr£ to the said seαon integrator (7) and by a -clock -generator αoni-ectec to 5. each said first and said second integrators (4-7) whereby to control the different time constants of the said integrators (4-7). 7. A signal processing device according to C f.ir- 6 • wherein the said clock generator (12) is con eccec to sy- -hror.ise with the said scanner. 8. A signal processing device acco__ding to Claim 5 or 6 charact-εrised by a low noise preaπplifier (2) connected to receive the signal from the said detector, and a bandpass filter (3) connected to receive the signal frαn the optical detector (1) and 5. pass the signal to the said first profile integrator. " 9. A signal processing device according to Claim 5 or 6 characterised by a σαtrparator (10) connected to receive the signal from the said first integrator (4) and the said second signal integrator (6) and to pass a processed signal to a tone 5. detector (11) . 10. A signal processing device constructed substantially as described and illustrated in the a xnpanying drawings.

Inventors: GAMBLING DAVID JOHN, WATSON RODNEY JAMES, GAMBLING, DAVID, JOHN, WATSON, RODNEY, JAMES
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE SECRETAR
Application year: 1985
Main classification: H04N7
IPC codes: G08B13