IMAGING METHOD AND APPARATUS

Abstract: A high resolution image detection and processing method and system use imaging devices (10) which generate analogue output signals that are representative of the energy distribution in the focal plane of the lens systems of the devices (10). These output signals are converted into digital format and stored in a random access memory (16). The data in the memory (16) is used by an image acquisition system (17), controlled by a microprocessor (21), and containing an image processing controller (18), to generate required images that are displayed on a monitor (20). The output signals of the imaging devices (10) may also be recorded in a video recorder (14). Wide angle surveillance systems are constructed using a plurality of imaging devices (10) mounted to have overlapping fields of view, or using an imaging device incorporating a fish-eye lens.

Description: TITLE: IMAGING METHOD AND APPARATUS FIELD OF THE INVENTION This invention concerns imaging. More particularly, it concerns high resolution surveillance systems using imaging devices which produce information in a manner such that the information can be stored and/or digitally processed, if required. The invention is particularly useful for ultra-wide field of view imaging and surveillance, but it is not limited to this application. BACKGROUND ART The commonest form of optical imaging and surveillance device which has an output that can be stored or processed, is the television camera. Such cameras are now used in surveillance ' systems for, inter alia, traffic control and security purposes (for example, in banks). Television cameras, however, have a relatively low image resolution. When greater image resolution is required, the optical imaging is usually effected by photographic cameras, or by photographic plates exposed under carefully controlled conditions (for example, in a tracking telescope when the image required is of a faintly-visible star) . The information contained in photographic images, however, cannot be processed readily and rapidly in the same manner as video data from a television camera. DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a system which enables optical images of high resolution to be obtained, and which can produce data which is representative of the high-resolution image and which can be stored and/or processed using a programmed microprocessor or another form of computerised processing equipment. To achieve this objective, the present invention provides an image detection and processing method and system in which an imaging device produces analogue output signals that are converted into digital signals, that are stored in a memory. The information in the memory is processed to provide a desired output signal for a monitor. Alternatively, or additionally, the output signal from the imaging device is fed via a video multiplexer to a video recorder. Thus, according to the present invention, there is provided a method of generating data which is representative of an image, the method comprising the steps of: a) producing analogue signals which are representative of the image; b) converting the analogue signals into digital signals ; c) storing the digital signals in a random access memory; d) processing data from the random access memory to produce signals representative of a required form of the image; and e) storing the signals produced by step (d) and/or using these signals to display the required form of the image. Also according to the present invention, there is provided an image detection and processing system which comprises : a) at least one image detection device having an output which is responsive to the distribution of the energy that is incident thereon; b) at least one video analogue-to-digital converter, adapted to receive the output from the image detection device or from at least one of the image detection devices; c) a random access memory, adapted to receive the digital output from the or each analogue-to-digital converter; d) an image acquisition system, adapted to receive data from the memory and perform functions therewith; and e) a control unit adapted to control the operation of the image acquisition system. Additionally (and optionally) the method of the present invention may include the steps of supplying the analogue signals which are representative of the image to a video mutliplexer and recording the signals from the video multiplexer in a video recorder. And the system of the present invention may include: a) a video multiplexer to which the output of the image detection device is supplied; and b) a video recorder, for recording the signals from the video multiplexer. Image acquisition systems which may be used in the system of the present invention are available commercially. The preferred form of image acquisition system comprises an image processing controller, a digital-to-analogue converter and a monitor to display the desired image generated by the output signals from the image processing controller. The functions that are typically performed by the image acquisition system include pattern recognition and image enhancement. The image detection device used in the system of the present invention is preferably a device which includes: a) an array of charge coupled devices (a CCD array) , or b) an image intensifier tube which is coupled to a CCD array either directly or through a fibre optic link, or c) a pyroelectric imaging array, or d) a thermal imaging array. If the system of the present invention is to be used for surveillance and a wide angle field of view is required, then a fish-eye lens arrangement may be used with the imaging device. Alternatively, a plurality of individual imaging devices, each having a relatively narrow field of view, may be mounted as a single unit to supply data to the random access memory. Other preferred features of the system of the present invention are the mounting of the device -in a housing which contains a window, to protect the device from the effects of a hazardous environment (such as sea water or corrosive gases or liquids), and, especially in the case of a wide angle surveillance system, the provision of a zoom facility to provide greater definition or resolution of a part of an image. These and other features of the present invention will become more apparent from the following description of embodiments of the present invention. In this description, reference will be made to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of an image acquisition and processing system which includes the present invention. Figure 2 is a partly-sectional, partly schematic illustration of an imaging device • hich has been used in a surveillance system. Figure 3 is a schematic representation of a 19-element optical surveillance device which has a field of view of approximately ^ steradians. Figure 4 shows, schematically, a fish-eye lens imaging device which also has a field of view of approximately 2"TC steradians. DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The system illustrated in Figure 1 has an image detection device 10 comprising an image observing arrangement 11 and a signal output arrangement 12. As will be shown later in this specificaton, the image observing arrangement may be a plurality of camera-like devices, or it may comprise a single camera. If a plurality of camera-like devices are used, there will be a corresponding plurality of signal output arrangements 12. The signals from the output arrangement 12 usually represent, in analogue form, the energy distribution of an image that is formed in the focal plane (image plane) of a lens system in the image observing arrangement 11. These signals are converted into digital signals by the analogue-to-digital converter 15, and are stored as digital signals in the random access memory 16. If there are a plurality of signal output arrangements 12, the analogue output signals may be multiplexed and converted to digital signals -by a single analogue-to-digital converter 15. However, if the system has to be used in a situation where it is important that the analogue signals from all the output arrangements 12 are read simultaneously into the random access memory 16, then each output arrangement 12 must have an associated analogue-to-digital converter 15. The signals stored in the random access memory 16 can be processed by an image acquisition system 17 which includes microprocessor 21. Microprocessor 21 controls access to the information stored in memory 16 by an image processing controller 18. As noted already, a number of image processing controllers are available commercially. The microprocessor unit 21 performs a controlling and decision making function regarding the operation of the image processing controller 18. The results of the processing of information by the controller 18 are displayed on a colour or monochrome monitor 20. The system shown in Figure 1 also includes the optional additional feature of recording the information from the image detection device 10 for subsequent display or processing. The analogue signals from the signal output arrangement (or arrangements) are multiplexed using video multiplexer 12 and stored in video recorder 14. One form of image detection device is illustrated in Figure 2. This device consists of an optically transparent window 25, a camera lens arrangement 26, a detection/intensification device 22 (to measure the energy distribution in the focal plane of the lens arrangement 26, where an optical image is produced), and an electrical or optical coupling system 23 which conducts the output information signals from the device 22 to the analogue to digital converter 15 of Figure 1. A preferred form of the device 22 is a two-dimensional silicon charge coupled device (CCD) array, which produces electrical signals when read out. Another favoured form of device 22 is an image intensifier tube, and if this is used in the imaging device, the coupling system 23 will normally be an optical fibre link between the output of the intensifier tube and a CCD array. Other suitable forms of image detection device may be used as the device 22 of Figure 2. BADQBIG-N^ The window 25 may be part of the camera lens system. Normally window 25 is sealed to an impermeable housing 24 to encapsulate the imaging device and protect it from the effects of a harmful environment, for surveillance and imaging systems incorporating the imaging device may be used for underwater surveillance or as optical monitors in locations containing corrosive gases or liquids. Those skilled in this art will be aware that using a two dimensional CCD array, or one of the noted alternative image detection devices, at the focal plane of the lens arrangement 26, enables a high resolution representation of the image to be produced from the output signals from the image detection device. The resolution, or instantaneous field of view of the detector elements in the imaging device, and consequently the resolution of the device, is determined by the angular field of view of the camera lens system in the device, and by the number of detector elements in the focal plane array, or similar image detection system. For example, with a camera lens system with an angular field of view of 24° focused on to a CCD array having 512 x 512 elements, the angular resolution or instantaneous field of view of a detector element is 0.8 milliradians, or 0.05°. As focal plane arrays with increasing numbers of elements become available, the resolution will be increased. The present invention is particularly useful when a surveillance or imaging system with an ultra-wide field of view is required. In such a situation, either the arrangement shown in Figure 3, or the image detection device illustrated in Figure 4, may be used in the system. If a wide angle surveillance system is created using devices of the type illustrated in Figure 2, a number of devices - which can be considered as surveillance modules - will be arranged in configurations which ensure that the fields of view of the individual modules overlap, to thereby produce a continuous field of view over any segment of a sphere. The device or module shown in Figure 1 has an angular field of view of approximately 24 . Thus a hemispherical arrangement of nineteen discrete modules 30 of this type, as shown in Figure 3, can p.rovide a surveillance system having a total field of view of approximately VT steradians. A spherical system having thirty-eight such modules can be produced with a field of view of almost 2 " Jf steradians. If the number of identical modules in such systems is increased, the angular field of view of each module can be reduced, with a consequential increase in the spatial resolution of each module. The alternative wide angle surveillance device illustrated by Figure 4 comprises a modified form of fish-eye lens 40, which focuses incident energy upon a shaped image plane 41. Fibre optic bundles 42 connect the image plane 41 to a CCD array 43. The output of the CCD array 43 is supplied to the analogue-to-digital converter 15 and/or the video multiplexer 13 of Figure 1. Another useful form of surveillance system which has been constructed using the present invention consists of twelve or more identical surveillance modules arranged on the outer surface of a support ring to provide a panoramic electro-optical camera of high resolution. This form of system is particularly useful for the intelligent control of traffic lights at busy street intersections. In some traffic situations^ adequate surveillance of a street intersection can be effected with a modified form of this panoramic electro-optical camera, containing only four or five imaging modules with non-overlapping fields of view. In surveillance systems using a plurality of imaging modules, each of the identical modules may be controlled, and their image information processed, by discrete microprocessor units to enable pattern recognition, signal processing and some decision making to occur. Such an arrangement has been shown in Figure 1 and has been described above. However, instead of using multiple microprocessors, the individual modules may be polled by a. single microprocessor. Such a configuration will be suitable when rapid scanning and decision making over large volumes is not required. A more powerful and flexible arrangement uses individual microprocessors for each imaging module, with a central controlling unit polling the individual microprocessors. The operation of the central controller may be interrupted by any module which observes the occurrence of a significant event. When the operation of the central controller is interrupted in this way, the information from the alarmed unit may be displayed, to enable critical decisions to be made and the relevant information to be recorded. For some surveillance applications, only low resolution images need be acquired until some significant event is flagged, whereupon the imaging system will be required to zoom to higher resolution. This form of system may be achieved when CCD arrays are used in the imaging modules. During the low-resolution monitoring, the signals from the module are sampled or averaged over regions of the array. When zooming is required, the number of elements sampled is increased or the number of elements averaged is decreased. It should be noted that -although, in this »_ specification, the term "optical" has been used, this does not mean that the present invention is limited to the imaging of electromagnetic radiation in the visible spectrum. It should also be noted that although specific embodiments of the present invention have been illustrated and described, variations and modifications of those embodiments may be made without departing from the present inventive concept. INDUSTRIAL APPLICABILITY The imaging method and surveillance system of the present invention have many potential applications. Some of these applications have been mentioned already. They include the observation and control of traffic at street intersections, security systems for financial institutions such as banks, and surveillance operations in hostile environments (such as chemical processing plants and underwater locations) where it is necessary to protect the observer from the environment, and where it is desirable to have no moving parts.

Claims: CLAIMS 1. A method of generating data which is representative of an image, the method comprising the steps of: a) producing analogue signals which are representative of the image; b) converting the analogue signals into digital signals; c) storing the digital signals in a random access memory (16) ; d) processing data from the random access memory (16) to produce signals representative of a required form of the image; and e) storing the signals produced by step (d) and/or using these signals to display the required form of he image. 2. A method as defined in claim 1, * including the additional steps of f) supplying the analogue signals which are representative of the image to a video multiplexer (13); and g) recording the signals from the video multiplexer (13) in a video recorder (14). 3. An image detection and processing system which comprises: a) at least one image detection device (10) having an output which is responsive to the distribution of the energy that is incident thereon; b) at least one video analogue-to-digital converter (15), adapted to receive the output from the image detection device or from at least one of the image detection devices; c) a random access memory (16), adapted to receive the digital output from the or each analogue-to-digital converter (15); d) an image acquisition system (17), adapted to receive data from the memory and perform functions therewith; and e) a control unit (21) adapted to control the operation of the image acquisition system (17). A system as defined in claim 3, in which the image acquisition system comprises: a) an image processing controller (18) adapted to receive information from * the random access memory (16) and to output digital signals in accordance with a predetermined function, under the control of said control unit (21); b) a digital-to-analogue converter (19) receiving the output of the image processing controller (18); and c) a monitor (20) receiving the analogue signals from the digital-to-analogue converter (19) and displaying the image represented by the output of the image processing controller (18). A system as defined in claim 3 or claim 4, in which there are a plurality of image detection devices (10) and each image detection device has its output connected to a respective analogue-to-digital converter (15), each said analogue-to-digital converter having its output connected to said random access memory (16). 6. A system as defined in claim 3 or claim 4, in which there are a plurality of image detection devices (10), and the outputs of said image detection devices are multiplexed and received by a single analogue-to-digital converter (15). 7. A system as defined in claim 5 or claim 6, for use in surveillance over a wide angle field of view, characterised in that the plurality of image detection devices (10) are mounted as a single unit, with the fields of view of adjacent image detection devices partially overlapping, whereby the system provides a continuous field of view over a required segment of a sphere. 8. A system as defined in claim 7, in which the number of image detection devices is selected so that the field of view of the system is substantially IF steradians. 9. A system as defined in claim 7, in which the number of image detection devices is selected so that the field of view of the system is substantially 2t steradians. 10. A system as defined in any one of claims 3 to 9, in which the or each image detection device (10) is a device which includes: a) an array of charge coupled devices, or b) an image intensifier tube which is coupled to an array of charge coupled devices either directly or through a fibre optic link, or c) a pyroelectric imaging array, or d) a thermal imaging array. 11. A system as defined in claim 3 or claim 4, for use in surveillance over a wide angle field of view, characterised in that the system includes a single image detection device (10), and said image detection device comprises: a) a fish-eye lens (40), adapted to focus incident energy upon a shaped image plane (41); b) an array (43) of charge coupled devices, providing the output of said image detection device; and c) bundles of optical fibres (42) connecting said image plane (41) to said array (43). 12. A system as defined in any one of claims 3 to 11, in which the or each image detection device (10) is provided with a zoom facility. 13. A system as defined in any one of claims 3 to 12, in which the or each image detection device (10) is located within a protective housing (24, 25). 14. A system as defined in any one of claims 3 to 13, additionally including: a) a video multiplexer (13) to which the output of the or each image detection device (10) is also connected; and b) a video recorder (14) adapted to receive and record signals from the video multiplexer (13). 15. An image detection and processing system comprising a) at least one image detection device (10) having an output which is responsive to the distribution of energy that is incident thereon; b) a video multiplexer (13) to which the output of the or each image detection device (10) is connected; and c) a video recorder (14) connected to said video multiplexer (13) and adapted to record the multiplexed signals from the or each image detection device (10).

Inventors: HONEY FRANK ROSS, HONEY, FRANK, ROSS
Applicants: TECH 21 PTY LIMITED, TECH-21 PTY LTD
Application year: 1986
Main classification: H04N7
IPC codes: H04N7