Imaging systems

An imaging system (10) comprises an imaging data-collection station (11) having a camera (15) with a field of view (16) mounted on platform (13) rotatable about azimuthal axis (14). Collected image data is delivered on line (20) to a monitoring station (12) together with data on line (19) representative of the angular position of platform (13) which is sensed by sensor (18). The monitoring station (12) incorporates at least one channel each channel having a display device (25) having a known display field (30, .alpha..sub.1), an operator-actuable sensor (26) which selects a particular angular position (.theta..sub.1), within the wide angle field (17) traversed by fixed field of view (16), a gate device (28) for capturing the pertaining image data from line (20) and a store (29) for storing captured data.

This invention relates to imaging systems. 
For security and other purposes there is frequently a requirement for a 
surveillance system which can be used to examine a wide angle field (often 
360.degree.). A problem which arises with such an arrangement is that the 
volume of image-data collected from the wide angle field when surveillance 
is undertaken for a lengthy time interval is so great as to cause major 
difficulty in interrogating the data. 
It is an object of the present invention to provide an improved form of 
imaging system capable of undertaking surveillance of a wide angle field 
and which obviates or mitigates the above-mentioned disadvantage. 
According to the present invention there is provided an imaging system 
comprising an image-data collection station and an image monitoring 
station, wherein said collection station comprises image-data collection 
means having a fixed field of view and means for effecting rotation of 
said field of view about an azimuthal axis whereby image data is 
continuously collected from a wide angle field, angle-sensing means 
associated with said rotation-effecting means for sensing instantaneous 
angular position of said fixed field of view within said wide angle field, 
image-data delivery means for continuously delivering collected image-data 
from said collection station to said monitoring station and 
angular-position-signal delivery means for continuously delivering said 
angular position signal from said collection station to said monitoring 
station, 
and wherein said monitoring station comprises a visual display monitor 
having a predetermined display field, an operator-actuable selector for 
selecting a particular angular position within said wide angle field and 
evaluating an associated range of angular positions within said wide angle 
field corresponding to said predetermined display field, data-capture 
means operable by said selector to capture repeatedly from the continuous 
delivery of image-data received by said monitoring station that image data 
from said associated range of angular positions, image-data store means 
connected to receive said captured data at each capture and to store 
captured data until the next data capture, the visual display monitor 
being connected to said store means to display the image data stored 
therein. 
It will be appreciated that in the imaging system of the present invention 
whereas image-data is continuously collected in the collection station the 
monitoring station only captures a small portion of the data and it is 
this small portion of data which is displayed on the monitor, the display 
being repeatedly refreshed by each newly-captured data. Also, because the 
selector is operator-actuable the image which is displayed on the monitor 
may be varied in position from time to time in accordance with the 
operator's wishes so that surveillance of different portions of the wide 
angle field is possible. Also, the monitor may incorporate a frame 
comparator to effect data comparison on a frame by frame basis and to 
provide an alarm signal to an operator in the event that the comparison 
indicates lack of identity between two frames. The wide angle field may be 
360.degree. wide and the rotation-effecting means may provide continuous 
unidirectional rotation or uninterrupted bidirectional rotation. 
The image-data collection means may operate in the visual or infrared 
waveband and may comprise a suitable camera (visual or infrared radiation 
sensitive) mounted on a rotatable platform. Alternatively the camera may 
be fixedly mounted and its fixed field of view rotated by optical means 
such as by a rotating reflector--for example a mirror or prism with a 
complementary image de-rotator prior to the camera. The fixed field of the 
camera preferably is elongate in the direction of the axis of rotation 
thereof and may in its simplest format simply be in the form of a line so 
that image data is collected from the line as it continuously passes 
around the wide angle field. The camera's fixed field is non-rotating. 
The pointing direction of the camera may be orthogonal to the axis of 
rotation of the field of view or it may be elevated or depressed with 
respect to orthogonal. 
In the monitoring station there may be a plurality of channels each 
provided with a visual display monitor, selector, data-capture means, and 
image-data store means arranged as previously described so that a 
plurality of operators may simultaneously monitor different (or 
duplicated) portions of the wide angle field. In this connection it will 
be appreciated that the data-capture means preferably does not extract the 
captured image data from the continuous delivery of image data but simply 
replicates the captured data so that the entirety of the continuous 
delivery of image data is available to each channel.

In the drawing an imaging system 10 comprises an image-data collection 
station 11 and an image monitoring station 12. Station 11 comprises a 
platform 13 which is rotatable in azimuth about an axis 14 and which 
carries an image-data collection means 15 having a fixed field of view in 
the form of a line 16 parallel with axis 14. Platform 13 is continuously 
rotated by a drive (not shown) at a rate which is known (for example 2 
revolutions/second), and accordingly line 16 moves in a circular locus and 
traverses a 360.degree. wide field 17. The angular position of the 
platform 13 is sensed by a sensor 18 which may be in the form or a synchro 
and an angle-position signal is delivered from the sensor 18 along lead 19 
to station 12 whilst image-data is continuously delivered along lead 20 to 
station 12. 
Monitoring station 12 comprises a plurality of channels 1,2,3, etc. of 
which only channel 1 is shown in the interests of clarity but it is to be 
understood that the other channels are similar. Channel 1 comprises a 
visual display monitor 25 having a predetermined display field the 
characteristics of which are therefore known and are represented by the 
parameter .alpha..sub.1. A manually-operable selector 26 functions to 
designate an angle .theta., relative to a datum direction 27 (see FIG. 2) 
from which the operator wishes an image to be displayed on monitor 25, 
.theta..sub.1 denoting a particular location within the 360.degree. field 
17. Selector 26 functions to combine parameters .theta..sub.1 and 
.alpha..sub.1 to determine a range of angular positions namely from 
(.theta..sub.1 -.alpha..sub.1) to (.theta..sub.1 +.alpha..sub.1) which 
range is applied to a gate device 28 in order to capture the corresponding 
portion of image data from lead 20, the captured data being delivered to a 
data store 29 the output of which supplies the image data to be displayed 
on the monitor 25. Accordingly the field 30 displayed on the monitor 25 
represents a portion of the field 17 located at a position denoted by the 
parameter .theta..sub.1 and determined in its angular extent by the 
parameter .alpha..sub.1 
It will be understood that a second channel, for example channel 2 may 
simultaneously display a field 32 located at .theta..sub.2 and of extent 
.alpha..sub.2 as shown in FIG. 2. 
The camera 15 may take any one of a number of configurations. For example 
it may comprise one or more radiation-detection elements and a line 
scanner providing a vertical line scan of about 30.degree.. Alternatively 
it may comprise an array of detector elements arranged in a plurality of 
lines thereby providing a plurality of simultaneous outputs each 
representative of one line in which case the revolution rate of the field 
of view and the vertical line scan rates are co-ordinated to provide for 
contiguity of the image-data over the 360.degree. field. The image data 
for example may be fed into a CCD having radiation sensitive stores so 
that successive items of image-data provided by the passage of successive 
detector lines over a fixed line within the 360.degree. field effects 
signal integration. 
The data store 29 may also take a variety of configurations and in 
particular may be of the type wherein the data is clocked out to the 
monitor 25 at TV raster scan compatible rate irrespective of the data 
clocking in rate which is determined by the characteristics of the camera 
15 and the revolution rate of the line 16 along the field 17,--i.e. scan 
converted. 
The displayed field as viewed in the monitor 25 may be less than that of 
the scanned field in vertical extent by signal processing at the store 29 
so that for example picture height is only half that of the scanned image 
height by display of only every second item of image data along the line 
16. Furthermore the store 29 may be arranged to store more items of data 
than the monitor 25 is capable of displaying selection of the data items 
to be displayed being governed by pitch, roll and yaw sensory signals 
derived from the support on which the camera 15 is mounted in order to 
provide for picture stabilisation. 
The camera 15 may alternatively comprise a frame transfer CCD having a 
radiation-sensitive image area on which radiation is incident for one 
field period to build up charge at the pertaining photosites. During the 
field blanking period of the monitor 25 when operating with a TV raster 
format the charge is transferred in the CCD from the image area to the 
non-radiation sensitive store area and during the following field period 
that stored data is clocked out at line frequency to an output register 
during line blanking, fresh data being collected in the image area. In 
this arrangement the clocking of data through the image area of the CCD 
and the store area of the CCD is effected at the same rate as the image 
(as distinct from the image data) is being moved across the image area so 
that integration of line information is effected by a factor of N where N 
is the number of lines contained in the CCD image area.