GB2166317A - Slow scan solid state television camera - Google Patents

Abstract

A television apparatus comprises a video camera 1 having a lens 4 for forming a light image upon a charge coupled solid state frame transfer device 6 having a store to which an image signal corresponding to the light image thereon can be transferred for electronic scanning to form a video image signal. Means are provided for causing the charge pattern formed in the image storage area of the frame transfer device 6 to be retained in a stable condition independently of the light image formed by the camera lens 4 to enable scanning of the image storage area at a slower rate than the conventional television image frame repetition rate, in order to derive a signal capable of being transmitted over a transmission medium having a narrow band width. Such means may include a shutter 7 located between the camera lens 4 and the frame transfer device 6 and a cooling device 8 for reducing the temperature of the frame transfer device 6. The shutter may be a pulsed proximity focussed image intensifier, allowing the device to be used at low light levels. The frame period may be between 20 and 110 seconds. <IMAGE>

Description

SPECIFICATION Improvements in and relating to television apparatus This invention concerns improvements in and relating to television apparatus, and more especially to apparatus, such as video surveillance apparatus, which enables scanning of a scene at a conventional TV rate, such that the resulting video picture can be transmitted over a longer period, through a transmssion medium having a relatively narrow band width.

In video camera apparatus, it is known to use a so called frame transfer charge coupled solid state image device, which comprises two near identical areas which respectively form an image area and a store. In normal operation, a scene is focused via a lens on to the image area, which is thereby continuously illuminated by the picture image, to produce a corresponding charge pattern over the image area of the device. The electrically defined image from the image area is then transferred into the store section at intervals corresponding to the required television frame frequency, and during the interval between each transfer, the information contained in the store is then extracted by scanning the store to produce a video signal. Examples of circuits controlling the formation and scanning of the charge-defined image are shown in U.S.A.

Patent Specification No. 3,931,463 and GB 2140651A.

Whilst the known arrangement provides an effective video camera, for operation at normal television frame frequencies, i.e. the European frame frequency of 50 Hz, or the USA or Japanese frequency of 60 Hz, the frame transfer device contains inherant functional limitations that mitigate against its use at lower scanning frequencies suitable for production of a narrow band width video signal.

For transmission of a video signal over a transmission medium having an available bandwidth of, for example, 3 KHz, in comparison with a conventional television signal bandwidth of approximately 6 MHz, it will be appreciated that, in accordance with the resolution required in the video image, a very substantial reduction in the frame scanning rate could be necessary, for example to, say between 20 and 110 seconds per frame. However, in the known arrangements the continuous illumination of the image area requires that a rapid frame repetition rate be used to limit charge spreading into the store area, whilst the relatively high noise and dark current that occurs within the store area between the instants of frame transfer are such that unacceptable deterioration of the stored image would occur over longer scanning periods.

Nevertheless, there is a requirement for a storage facility to enable reduction of the band width required for the transmission of video signals derived from such a camera, and in hitherto known arrangements, considerable supplementary storage and processing equipment are provided in order to modify the resulting video signal to the extent that it is capable of being transmitted over a narrower band width transmission medium, such as a conventional audio or telephone cable. Such known systems are not only expensive but are of a large size.

Accordingly, it is an object of the present invention to provide a system enabling the derivation of a video signal having a slow scanning rate directly from a more compact and unobtrusive video camera.

The invention accordingly provides a television apparatus comprising a video camera including a charge coupled frame transfer solid state image device having an image receiving area, an image storage area, and charge coupling means for transferring image patterns from said image receiving area to said image storage area to enable a video signal representative of an original image to be derived by scanning the said storage area; a camera lens for focussing light images upon said image receiving area to form a corresponding pictorial charge pattern thereon; and means for causing a corresponding charge pattern formed in said image storage area to be retained in a stable condition independently of the light image formed by said camera lens for a length of time sufficient to enable scanning of the image storage area at a rate substantially below that required to produce a video image frame signal at a conventional television frame frequency.

In accordance with one aspect of the invention, a video camera of the kind incorporating a frame transfer solid state image device is provided either with a shutter located between the camera lens and the image area of the device or, by suitable drive clocks to the image area, whereby through operation of the shutter or clocks at a desired, relatively low, frame repetition rate, corresponding picture images can be formed on the image area of the frame transfer device. This technique is similar to the technique described in USA 3931463 and GE 2140651A referred to above but differs from them insofar as the technique is not used to generate a standard video signal, but only a "charge clear" mechanism.One of these images is rapidly transferred to the storage area, and means is provided for scanning the storage area of the device at a correspondingly slow rate between individual exposures of the image area, in order to derive a resulting video signal of correspondingly low band width for later coding.

In accordance with a second aspect of the invention, the frame transfer image device is subjected to cooling to reduce the noise and dark current obtaining within the storage area of the device to a level at which an image of acceptable resolution can be read from the storage area over a period corresponding to the desired coding speed.

The invention is illustrated by way of example in the accompanying drawing, the single figure of which is a block diagram illustrating a device in accordance with the invention.

Referring to the drawing, the box shown in broken lines at 1, represents a video camera, in accordance with the invention, the box 2, a reproduction system for displaying the video im age, and the lines 3, a transmission medium linking the two units.

The camera 1 comprises a lens 4, by means of which an image 5 may be focussed on the image area of a solid state frame transfer device 6, of known type. Between the lens 4, and the frame transfer device 6, is optionally located a shutter 7, which may be a mechanical or electronic shutter, but is preferably a so-called pulsed proximity focussed image intensifier, which provides both a shutter function and automatic image intensification, thus allowing the system to be used in very low light applications. Such focussed image intensifiers are known, being sold, for example, under the trade name "Proxitronic" by the firm of Funk GmbH. A cooler 8, for example of the thermoelectric Peltier type, serves to reduce the temperature of the frame transfer device 6, which is preferably thermally insulated by location within an evacuated glass envelope, not shown.

Reference 9 designates an electronic circuit which controls operation of the frame transfer device 6 and the shutter 7, and controls the read out of the image from the store area of the frame transfer service 6 and codes for transmission.

Thus, for example, the shutter 7 may be operated at intervals of up to approximately 40 seconds, the resulting image being transferred from the image area to the store of the frame transfer device, following each exposure, and then being read out by the circuit 9 in the form of a transmittable and codable video signal. The selected interval between consecutive exposures effected via the shutter 7 will depend upon the desired resolution of the video picture to be transmitted, the bandwidth available in the transmission medium 3 and chosen transmission code. Typically between 20 and 110 seconds will be required for scanning each image frame, whereas the formation of the picture image and its transfer to the image store area will be effected at the conventional TV frame frequency.

The video signal reproduction apparatus 2 comprises a video receiver and decoder 10, an image store 11, a display monitor 12 and/or a printer 13 for reproduction of transmitted images in document form.

The camera unit 1, as described above, is capable of providing a video signal having a low frame repetition rate and capable of being transmitted via a transmission medium of low band width, whilst being of compact construction. The picture signal intermittently formed in and transmitted from the charge coupled frame transfer device 6 can thus be transmitted by the receiver 10 and stored in the image store 11 for reproduction on the display monitor 12. The image store 11 holds the signal as a stationary TV picture for display on the monitor 12, this picture being held until a new one is transmitted from the camera 1 and built up within the store 11. On completion of the new picture within the store the monitor 12 is then refreshed with the latest up-date.

It will be appreciated that be the elimination of bulky image storage equipment, as required in conventional transmitting apparatus, the arrangement according to the invention can advantageously be utilised in many applications. For example, portable and unobtrusive video camera equipment could be clipped to the lapel of a police officer's or soldier's uniform, improving his ability to remotely communicate picture signals over low quality audio transmission channels. Other applications might include, for example: (a) Identity checks by banks, at either counter or cash dispenser; (b) Transmissions over long cable in oil wells and borehole investigations by TV; (c) Subminiature and portable facsimile machines; (d) Video phone on existing telephone network; (e) Remote personal identity checks; (f) Alternative low cost facsimile reproduction using existing telephone network; (g) Remote news gathering and (h) Transmission over long cables for remote area surveillance purposes, possibly in conjunction with movement sensing equipment.

Claims (10)

1. A television apparatus comprising a video camera including a charge coupled frame transfer solid state image device having an image receiving area, an image storage area, and charge coupling means for transferring image patterns from said image receiving area to said image storage area to enable a video signal representative of an original image to be derived by scanning the said storage area; a camera lens for focussing light images upon said image receiving area to form a corresponding pictorial charge pattern thereon; and means for causing a corresponding charge pattern formed in said image storage area to be retained in a stable condition independently of the light image formed by said camera lens for a length of time sufficient to enable scanning of the image storage area at a rate substantially below that required to produce a video image frame signal at a conventional television frame frequency.

2. A television apparatus as claimed in claim 1 in which said image stabilising means includes a shutter disposed between said camera lens and the said image receiving area.

3. A television apparatus as claimed in claim 1 or 2, in which said image stabilising means includes a cooling device for reducing the ambient temperature of said image storage area of the frame transfer device.

4. A television apparatus as claimed in any one of claims 1-3, in which said image stabilising means includes means for intermittently actuating said image receiving area of said frame transfer device, whereby the formation of charge patterns thereon is inhibited during scanning of said image storage area.

5. A television apparatus as claimed in any one of claims 1-3, in which said image stabilising means includes means for disabling said charge coupling means during scanning of the image stor age area.

6. A television apparatus as claimed in claim 3 in which said frame transfer device and said cooling means are located within a common thermally insulating enclosure.

7. A television apparatus as claimed in any one of Claims 1 to 6 incorporating means for transmitting a video image signal derived by scanning of said image storage area.

8. A television apparatus as claimed in Claim 7, in which said means for transmitting said video image signal incorporates means for encoding said image signal prior to transmission.

9. In combination with a television apparatus as claimed in Claim 7 or 8, a television signal receiving apparatus including means for storing image data corresponding to a complete image frame of a video signal transmitted from said television apparatus, means for receiving a said transmitted signal and transferring to said store the image dates corresponding to each complete frame signal, and means, coupled to said store, for displaying a stationary picture image corresponding to the last complete image frame signal contained in said store, during refreshing of said store by a newly received television image signal.

10. A television apparatus substantially as described herein with reference to the accompanying drawings.