Patent GB-1401179-A (GB)
Title: Automated image analysis employing automatic fucussing
IPC: G01N21/27
Filed: 1971-09-22
Abstract: 1401179 Automatic focussing IMAGE ANALYSING COMPUTERS Ltd 18 Sept 1972 [22 Sept 1971 28 June 1972] 44132/71 and 30278/72 Heading H4D In an automatic focussing system such as shown in Fig. 10 of Specification 1,325,439 wherein 500 different areas of a microscope specimen are sequentially viewed by a television camera and the resultant video signals are used in the automatic focussing system as well as in the specimen analysis, the focussing of each area may take À5 seconds, resulting in a time of 250 seconds for the focussing of the whole specimen. This time is five times that required (50 seconds) for the total analysis. To overcome this sixfold time increase, only every nth area is focussed, the focussing values for the intermediate areas being kept the same as the last nth area. When the areas are scanned in a raster pattern, the areas at the beginning of each line are additionally focussed. The focus value for the first area of one line is carried over for use on the first area of the next line, thereby reducing the amount of refocussing. In the arrangement of Fig. 4, opposite polarity versions of the video signal are produced by phase splitting amplifier 79 and these are differentiated at 80 to produce pulses for both leading and trailing edges of the video signal. To take account of the amount of detail in the scanned area, the differentiated signal is compared with a variable threshold at 81. Each pulse greater than the threshold is converted to a standard height/width pulse by mono-stable 93 and accumulated at 94 to provide a threshold signal via store 96 and potential 97 proportional to said amount of detail. The threshold is established during the first area scan and then held and repeated at 96 for the remaining (n- 1) area scans. An end of frame EOF pulse is counted in frame selection 77 to give a pulse every nth area for the opening of gate 78 and the passage of the comparator 81 output to an accumulator 82. A threshold comparison, at 84 of the accumulator output, detects if the focus is so bad that less than a certain number of detail features are detectable in the video signal. Manual refocussing is then called for. The log of the accumulator output is fed to comparator 86 and to n frames period store 87 which provides the second input to the comparator, a comparison is thus made between the degree of focus of two successive nth areas A and B. A system 88, 89 analyses the comparison and decides what refocussing, if any, is required. In the arrangement of Figs. 5a and 5b a control circuit 200 enables gate 152 and so passes the video signal from T.V. camera from either every nth area (EON signal) or at the first area of line (end of line EOL signal) to the focus measuring system 132. A store 138 enables the comparison at 140 of the degrees of focus FF1, FF2 of successive nth or beginning of line frames. The results of the comparison being fed (Fig. 5b) to a control circuit 142 which produces, in focus INF, out of focus, OOF, signals as well as signals for the focussing motor 75. A store system 222, ensures that the same degree of focussing is used for the rest of the (n-1) areas or rest of line. The end of n areas and end of line signals EON, EOL, are produced by counters 182, 190 counting the number of stepping pulses to the line stepping motor 30<SP>1</SP>.