GB2175768A - Television camera far viewing high speed or transient events - Google Patents

Abstract

A television camera arrangement includes a plurality of image sensors 9, 10 e.g. MOS semiconductor arrays each of which responds in turn to a flash of light gated by image intensifier 3, constituting an image of a viewed scene. Sensors 9, 10 are made responsive to alternate flashes of light and video signal outputs of the image sensors are combined 19 to produce a composite video signal containing contributions from all image sensors, so that it in effect corresponds to a television system operating at a higher frame rate. The arrangement is particularly suitable for viewing high speed or transient events, and for generating a video signal which is representative thereof. If a signal transmission path of sufficient bandwidth is available the video signal outputs of the image sensors may be transmitted separately and sequentially. More than two image sensors may be used (Fig. 4). <IMAGE>

Description

SPECIFICATION Television camera arrangement This invention relates to a television camera arrangement, and is applicable to such an arrangement which is suitable for generating a video signal containing information about a field of view which includes high speed or transient events. In order to capture very short-lived events, or the detail of a rapidly changing scene, a high television field rate is required. The nature of the electro-optic sensors available for television cameras serves to restrict the upper limit of speed of operation, as solid state image sensors in particular require a significant amount of time to output a video signal. It has therefore been customary to use a high speed cinematographic film to optically record rapidly occurring events.

This invention seeks to provide an improved television camera arrangement which is inherently capable of fast operation.

According to this invention, a television camera arrangement includes a plurality of image sensors each arranged to share a common field of view; and means for operating the sensors at a given field rate so that they respond in turn to the field of view so as to produce a signal representative thereof; and means for combining the signals to produce a composite video signal having an image content corresponding to Rn effective frame rate which is higher than that of said given rate.

Preferably the video signals from the image sensors are interleaved to produce composite video signals containing recurring contributions from each image sensor.

Preferably again the plurality of image sensors are each arranged to produce an image of the same field of view from an optical image splitter which shares the available intensity of illumination of the image equally between the available image sensors.

The image sensors receive a shuttered, or intermittent, image of the field of view, each image sensor optically receiving all shuttered images, but being arranged to generate a utilised video output signal in response only to selected ones of the shuttered images. Thus, by opening a shutter momentarily, a short flash of light is produced which contains the image of the field of view.

The nature of the composite video signal will depend on the purpose for which the camera arrangement is used, and the nature of the path over which the video signal is to be sent. If the path has a very wide bandwidth the composite video signal may consist of a succession of discrete frame signals occurring at a rate which is higher than the conventional rate, the increased rate being dependent on the number of available sensors from which the individual outputs are interleaved. If, however, the available bandwith of the path over which the composite video signal is sent is not wide, and cannot accommodate more than the bandwidth associated with a conventional video signal, then successive fields are combined so that the information content from, say, four fields are combined on to a single television field.In this latter case, the information content may not be degraded to any significant extent since the nature of the combination of the individual field is such as to preserve the original contrast, definition, grey scale, etc.

The invention is particularly suited for the viewing of fast moving bodies, and in this event the combination of four successive fields to produce the composite video signal results in four displaced images being projected simultaneously in the reconstituted television picture, and this aspect can in fact assist in the interpretation of the nature of the body and its path.

The invention is further described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic implementation of a television camera arrangement.

Figures 2 and 3 are explanatory diagrams, and Figure 4 shows part of a modified implementation.

Referring to Fig. 1, the television camera arrangement shown therein includes a wide angle fish-eye lens 1 which surveys the external field of view and utilises a relay lens 2 to form an image thereon on the input surface of a gated image intensifier 3. The image intensifer is such as to produce a high intensity replica of the image at its input surface, but this high intensity output image is present only whilst a gate signal is present on lead 4. In this instance, short pulses of 10,as duration are applied to the lead 4 to gate on the imac intensifier. Such pulses are shown in line a OT Fig. 3 and they occur at intervals of 5 mS.

The output image is transferred via a further relay lens 5 to an optical beam splitter 6 consisting of two transparent glass prisms 7, 8 which share the incident intensity equally between two image sensors 9, 10. Each image sensor 9, 10 constitutes the image receiving surface of a television camera, the associated circuitry of which is represented by the blocks 11, 12. The respective image sensors 9 and 10 respond respectively to alternate fields, each field corresponding to a flash from the image intensifier, and the analogue field signal is fed via an analogue-to-digital converter 13, 14 and data control circuits 15, 16 to a field address circuit 17 which routes the field signal correctly into a field store 18.

Each image sensor is an MOS semiconductor device which is operated at a rate of 100 fields per second, which is twice the normal rate of a conventional broadcast television system. The sensors may be a frame transfer array of type P8602 available from English Electric Valve Company Limited, Chelmsford, Essex. The outputs from the two sensors 9 and 10 are utilised in turn, and this is represented by the field synchronising pulses shown at lines b and c of Fig. 3 for image sensors 9 and 10 respectively. The two prisms of the beam splitter share the available light equally between the two sensors, and this light is provided by the fast acting gated image intensifier, which opens for a duration of 10 fis at intervals of 5 mS.The short period of 10 ,ltS effectively freezes any fast movement occurring within the field of view of the lens 1.

As each sensor is required to ignore alternate flashes of the image, one or the other is back clocked immediately after the operation of the intensifier 32. The operation of a frame transfer image sensor 9 or 10 is explained with reference to Fig. 2, in which the sensor has an active area 21 upon which the image falls; this area contains a very large number of image sensing points, often termed pixels, arranged in lines and columns in the manner of a television raster pattern. One such line 22 and column 23 are illustrated, although typically over 500 lines are present. In response to a flash of light, charge is accumulated at each pixel site, and this charge is transferred by a forward clocking operation to a store area 24, which is similar to, and equal in size to, the image area 21.Forward clocking simply transfers each column of charge to similar columns of pixels in the store area 24, and so this is represented by the arrow 25. Subsequently, each row in the store area 24 is transferred one at a time to a read out area 26 (transfer being indicated by arrow 27), so that each row is then output sequentially via lead 28. Thus the normal operation, and the read-out period for sensor 9 is represented by the first positive pulse at line d of Fig. 3.

However sensor 9 is required to ignore the flash 30 of the intensifier, and this is achieved by back clocking. This means that the charge accumulated at the pixel sites of sensor 10 are clocked in to the dead area 29 shown in Fig. 2-charge transferred into this area is simply discarded as this area is connected to ground. The sensor 10 is then free and available to respond to flash 31 and produces a read-out pulse 32 at line e in response thereto, whereas sensor 9 is back clocked so that it does not respond to flash 31.

The read-out pulses, each of which represents a field of serial analogue signal, are passed via analogue-to-digital converters 13, 14 to the data control circuits 15, 16 which discard irrelevant data. Use of the fish-eye lens 1 produces a circular image area, whereas each sensor has a rectangular image receiving area, about 40% of which is therefore unused. Circuits 15, 16 simply discard the video signals relating to this unused area, and the remainder of the video signals are fed via field store address circuit 17 to a vacant location in the field store 18.

The third and fourth flashes 33, 34 produce read-out pulses 35, 36 (at lines f amd g) from sensors 9, 10 which are also read into the field store 18, which now contains four fields of video information, each related to events occurring at successive intervals of 5 mS.

These four fields are algebraically summed by a digital gate 19, and the resulting composite video signal which is shown in line h is output at port 20. The action of the algebraic summation is to combine the four fields into a single field so that the four images are superimposed but without loss of contrast or modification of the intensity scale as would be the case with optical superposition of four images.

This composite video signal has the bandwidth of just a normal television signal but contains fields occurring at a rate of 200 fields per second, so that the effective rate has been doubled by using the two image sensors 9, 10, each of which operates at 100 fields per second, which is twice the conventional television field rate. This enables fast moving bodies or transient events to be more clearly analysed, and the field rate can be increased even further by using additional image sensors, as is shown in Fig. 4. If a very high bandwidth output link is available, then the output composite video signal consists of each field transmitted separately and sequentially, so that the gate 19 is not used.

Referring to Fig. 4, incident light from the gated image intensifier is received by a first beam splitter 40, and is split equally between two further beam splitters 41 and 42, each beam splitter being similar to beam splitter 6 of Fig. 1. The output port of each beam splitter 41 and 42 is coupled via a fibre optic plate 43 to a respective image sensor 44, 45, 46, 47, and a similar fibre optic plate 43 is positioned between the beam splitter 40 and the two beam splitters 41 and 42.

Outputs of the four image sensors 44, 45, 46, 47 are utilised in turn in a manner similar to that already described for the two image sensors shown in the preceding Figures, so as to provide the required composite video output signal.

Claims (9)

1. A television camera arrangement including a plurality of image sensors each arranged to share a common field of view; and means for operating the sensors at a given field rate so that they respond in turn to the field of view so as to produce a signal representative thereof; and means for combining the signals to produce a composite video signal having an image content corresponding to an effective frame rate which is higher than that of said given rate.

2. An arrangement as claimed in claim 1 and wherein the video signals from the image sensors are interleaved to produce composite video signals containing recurring contributions from each image sensor.

3. An arrangement as claimed in claim 1 or 2 and wherein the plurality of image sensors are each arranged to produce an image of the same field of view from an optical image splitter which shares the available intensity of illumination of the image equally between the available image sensors.

4. An arrangement as claimed in claim 3, and wherein the optical image splitter includes a pair of transparent prisms each arranged to direct half the available illumination to a respective one of two image sensors.

5. An arrangement as claimed in any of the preceding claims and wherein each image sensor is adapted to generate an analogue video signal, and an analogue-to-digital converter is provided to produce a digital signal therefrom, prior to the production of said composite video signal.

6. An arrangement as claimed in claim 5, and wherein the digital signal from each image sensor is read into a store, from which it is read out in conjunction with digital signals from all of said image sensors so as to form said composite video signal.

7. An arrangement as claimed in any of the preceding claims, and wherein a field period of said composite video signal includes contributions from all of said sensors.

8. An arrangement as claimed in claim 7 and wherein a field period of said composite video signal includes contributions from a plurality of field periods from each of said sensors.

9. A television camera arrangement substantially as illustrated in and described with reference to the accompanying drawings.