Patent GB-1405881-A (GB)
Title: Information selection in image analysis systems employing line scanning
IPC: G09G5/38
Filed: 1971-08-07
Abstract: 1405881 Image analysis IMAGE ANALYSING COMPUTERS Ltd 3 Aug 1972 [7 Aug 1971] 37226/71 Heading G1A [Also in Divisions G4 and H4] The invention concerns a method of modifying the video signals corresponding to a selected region or feature of a field in, for instance, a line scanning image analyzing system such as is described in Specification 1264804. In Fig. 1 a camera 14 views a field 12 and produces an image thereof on a C.R. tube 10; the video signal is also converted to a two state signal at 66 for application to the anti-coincidence and parameter computing circuits of the analyzing system. On the face of tube 10 or on an overlay 26 can be drawn, e.g. with a crayon, a frame around the region selected. The tube is viewed by a photo-multiplier 20 thus acting as a flying spot scanner to generate a video signal representing the image on the tube face with the drawn in frame. A variable gain amplifier 32 (or an adding amplifier - Fig. 12 (not shown)) eliminates from this the image content and the signal representing the frame only is applied to a thresholding device 34 to produce a two state signal which comprises pairs of pulses representing intersections with the two sides of the frame. At 42, which comprises a bi-stable device, Fig.9 (not shown), or an arrangement of delay lines, shift registers, &c, Fig.10 (not shown), the signal is converted to long gating pulses which may be applied to an OR-gate 74 which adds them into the video signal. A second channel including a photo-multiplier 44 generates similar gating pulses from a further frame drawn on the screen in a different colour, or, Fig.3 (not shown), a different density, and these pulses are applied to an AND- gate 76 to effectively remove portions of the video signal from the camera. The two channels together can thus be used to modify any image in the field before it is applied to the analyzing circuits. The modified field may be viewed using a feedback path 71, 62. In order to overcome the effects of ambient lighting the tube 10 may produce an ultraviolet image in addition to the visual one; the crayons are opaque to two different wavelengths of ultraviolet and the photo-multipliers are made sensitive only to these wavelengths. In a modification, Fig.7 (not shown), the crayons are replaced by a light pen. This picks up the scanning lines on the tube 10 as it is moved around and produces an image of the frame only on the target of a scan-conversion storage type of C.R. tube (236) which, when the pen has described a complete frame, generates a video signal representing the frame only which is employed as before. Two or more frames can be distinguished by varying the brightness of the tube. The light pen could also be replaced by any form of X-Y co-ordinate generator such as a joy-stick which could be used to produce the frame image. In a further modification, Fig.4 (not shown), the light pen has only to be applied to three points on the tube 10, the co-ordinates of which are stored in individually selected registers and then used to generate electronically a rectangular frame with the points at three of its corners. Or, Fig.6 (not shown), just two points, at the centre and somewhere on the periphery of a desired square frame. Or, Figs.18-19 (not shown) an octagonal frame may be generated. The generated frame is displayed on the C.R. tube as it is produced. Extra registers can be provided'to separately store as many different frames as are required, all fed by a single light pen via selector switches. The individual registers can be replaced by a single addressable memory, Fig.8 (not shown). In another modification, Fig.13 (not shown), which avoids the need for amplifiers 32, the image is simply switched off while the frame is read. The switching may automatically apply the image to the tube 10 on alternate frames only and read the frame during the other frames when the tube shows a blank white field. In another modification, Fig.17 (not shown), various frames are drawn, all of the same colour or intensity and marked with one, two, three . . . &c. strokes which are then also read by the electronics to identify particular frames. This can be used in a shape classifying system where individual features are ringed and marked and then automatically counted according to the classifying marks.