Patent GB-1473684-A (GB)
Title: Scanning system for location and classification of patterns
IPC: G06V10/10
Filed: 1974-10-07
Abstract: 1473684 Pattern recognition GEOMETRIC DATA CORP 7 Oct 1974 [12 Oct 1973] 43366/74 Heading G1A Apparatus for recognizing a member of a predetermined class of patterns in a field containing a plurality of classes of patterns comprises: means for scanning in a first direction at a fast rate and in a second direction at a first slow rate; means for generating signals representing the density of colours detected at scanned positions; means for recognizing, on the basis of colour, density and size of the pattern, when the scan has arrived at a member of said predetermined class; means responsive to the recognition for backing off the scanning means in the second direction and for scanning the pattern in the second direction at a second slow rate slower than the first slow rate. Scanning and measurement For recognizing an eosinophil or neutrophil red-stained, leucocyte in a blood smear treated with Wright's stain on a slide 26, a CRT 20 and microscope lens system provide a flying spot for scanning a selected area about 300Á square on the slide 26. Dichroic elements 52, 54 and mirrors 56, 58 direct red, green and blue components of transmitted light to respective photo-multipliers. A colour processor and quantizer 30 detailed in Fig. 13 (not shown), provides digital signals representing the green, the blue/green difference and the red/blue difference respectively, which are used to ignore red cells and foreign matter, and to recognise an object which may be the blue-stained nucleus of a normal or abnormal leucocyte, on a platelet. A pattern capture device 36, and Fig. 14 (not shown), resolves the ambiguity by comparing the blue/green difference signals with Y-shaped reference pattern about 2Á wide by 1Á high Fig. 3 (not shown), accepting those which fit as indicating the presence of a leucocyte requiring further investigation. Search scan mode A scanner control 46 and Figs. 16 and 17 (not shown) signals the CRT to generate a raster of 300 vertical lines in an area about 3" square, which is reduced to about 300Á square at the slide 26. Successive lines are stepped 1Á to the right by a slow scan control. A platform control 44 may shift the slide platform 24 300Á to the left between frames. Detector signals are sampled at points spaced at 0.5Á along the lines by 1.5 MHz clock pulses generated by a timing unit 42, and Fig. 9 (not shown). Rescan mode As soon as a dark blue-stained point is detected the pattern capture device 36 is alerted; and if during this and the three successive lines the signals fit the Y pattern, the pattern capture device 36 puts the scanner control 46 and a window control 34, and Fig. 15 (not shown) in a rescan mode wherein the scan is modified thus: (a) The abscissa of the vertical line, which occurred just before the capture device 36 was alerted, is stored, i.e., four lines to the left of the point where conclusive evidence was received. (b) The slow scan is backed off a further 7Á to the left, and a ramp generator causes successive vertical lines to be spaced by 0.25Á for a width of 20Á. (c) For a height of 32Á symmetrical about the ordinate at which the nucleus was recognised, the signal sampling rate is doubled so as to reduce the vertical sample spacing to 0.25Á. (d) Information received from the quantizer 30 during the window thus defined is passed to a main shift register 32, and Fig. 7 (not shown) and thence, during line flyback, to a pattern recognition circuit 38 which feeds signals representing the presence and condition of the leucocyte to a computer 40. Resumption of search scan mode At the end of the rescan the search scan mode is resumed at the line whose abscissa was stored at the beginning of rescan. Since the leucocyte which initiated the rescan will now be scanned again, repetition of capture is avoided by, a timing and mode control unit 42, and Figs. 11 and 12 (not shown) which provides signals to the window control 34 and pattern capture device 36, to inhibit a further pattern capture during that frame in an area 48Á high by 24Á wide, wherein the nucleus was first detected in the middle third of the lefthand edge. Pattern capture is not, however inhibited at other points on the band of lines passing through that area.