Patent GB-1179823-A (GB)
Title: Imaging Systems
Inventor: GUILDFORD LESLIE HENRY
IPC: H04N7/00
Filed: 1968-05-08
Abstract: 1,179,823. Television. MULLARD Ltd. 8 May, 1968, No. 21788/68. Heading H4F. An imaging system in which all the picture elements of a scene are reproduced once during a frame, each frame comprising at least two fields consecutively scanned in opposite directions by an array of detectors each of which is sampled in a pseudo random manner relative to the field motion such that each detector is sampled once for every picture element it traverses during a frame. The system allows the use of a slow scanning speed, the pseudo random nature of the replenishment information providing a flicker-free picture without apparent motion of the replenishment information. The field of view of an embodiment of the system is illustrated in Fig. 1 and comprises 256 picture elements in the vertical direction and 253 picture elements in the horizontal direction. The scene is scanned horizontally by a mirror which directs the light on to an array of 256 detectors, the scanning being in alternate directions. The detectors are sampled in a pseudo random pattern, each detector being sampled once while the array scans 10 picture elements in the horizontal direction. The sampling pattern for some of the detectors is indicated by the crosses in the first area 1 of the Figure. The same sampling pattern is repeated in each succeeding area of 10 horizontal picture elements. After the first three horizontal elements of the 26th area have been scanned the end of the field is reached and the scanning direction is reversed so that this area comprises the last three horizontal elements of the first field and the first seven horizontal elements of the second field. The sampling pattern in this area is the same as before and the horizontal scanning continues in alternate directions, one of the pattern areas being folded on itself at the end of each field. The last area of the tenth field is area 253, the scanning of which finishes exactly at the edge of the field and forms the end of the frame. Since each detector is sampled once during each area scanned the sampling pattern may be selected so that every picture element is sampled once during the frame. As shown, Fig. 3, a scene 6 is scanned by means of a mirror 7 and an in-line array 5 comprising the 256 detectors. The detectors are connected via individual channel amplifiers 8 to multiplexing gates 9 in an order determined by the sampling pattern. The multiplexing gates provide outputs from the even- and oddnumbered gates to group selectors 11, 12 and video amplifiers 13, 14 the outputs of which are combined by a high-speed gate 15 and used to drive a display device 17 via a main video amplifier 16. A clock pulse generator 19 drives a pseudo random scanning generator which comprises an eight-stage binary counter 21 and a D/A converter 22 which provides 256 discrete voltage levels to provide the vertical deflection of the display device 17. The counter 21 is also fed to a binary/decimal decoder 23 which controls the gates 9, selectors 11, 12 and gate 15 via sampling drive circuit 10 to provide the desired sampling pattern which is synchronized with the vertical deflection of the display device 17. The horizontal deflection is provided by circuit 18 which is synchronized with the scanning mirror 7. The detectors may be sensitive to I.R. or visible light and may be arranged in an in-line or staggered manner, and the scanning direction may be at right angles to or at an acute angle to the line of detectors.