GB1504685A - Subtractive image analysis - Google Patents

Abstract

1504685 Subtractive image analysis IMAGE ANALYSING COMPUTERS Ltd 17 Feb 1975 [21 Feb 1974 23 Feb 1974] 7995/74 and 8346/74 Heading G1A In a subtractive image analysis system a field (a microscope slide) containing features to be investigated is imaged via a microscope 10 on to a television camera 12. The resulting video signal is passed via a threshold detector 14 (to produce constant amplitude pulses) to a gate 20 that is also supplied by an oscillator 18. The oscillator 18 provides a series of shorter duration constant amplitude pulses and so the gate's output represents a series of points (picture points, p.p.) which lie along each scanning line across the feature image. The picture points are supplied to a counter 26 which is reset in the absence of a picture point. The numerical count value in the counter 26 is compared after each picture point with a selected number n in a digital comparator 30. If the count value is greater than or equal to "n", a "1" signal is produced which may be counted on a counter 34 by turning a switch 36 to position 1. Thus the system is able to detect the number of times that the horizontal inspection strip ("n" picture points long) is able to be fitted into the feature area of the image. The system can be extended into two dimensions by further circuits, some of which is shown on Fig. 1 providing an "effective" regular octagonal inspection shape Fig. 2 (not shown). The number of times that this octagonal shape fits into the feature can be counted. The octagonal inspection shape is achieved by means of three counting circuits (only two shown) formed from shift register memories 34, 34' whose inputs are connected to its outputs via an adding stage 38 and a subtractive stage 40. One 35 of the shift registers is designed to provide a delay of one scan line duration to produce the "vertical erosion" part of the octagonal shape. Whereas the other two registers are designed to provide a delay of one line scan duration plus or minus one "picture point" in order to dilate or erode the inspection shape that is, provide the sloping portions of the octagonal shape. The description includes an alternative logic system Figs. 3-12 (not shown). Also in this system the equivalent to counter 26 counts "down" from a fixed member N instead of up to N. The alternative system therefore uses less complicated elements since the erosion or dilation techniques performed on the output from the comparator 30 are designed to count down from a predetermined number to tell when a particular erosion process has been completed (assuming a picture point being absent).