GB1277014A - Detection device for detecting outline features for image analysis systems - Google Patents

Abstract

1277014 Image analysis IMAGE ANALYSING COMPUTERS Ltd 29 April 1969 [1 May 1968] 49558/71 Divided out of 1277013 Heading H4F Relates to a detection device for use in an image analysis system employing line scanning arranged to detect boundary density variation and determine whether the scanning inspection spot is inside or outside a boundary feature, e.g. an annulus or ring as shown in Fig. 2 which does not have a different grey level within the boundary from that outside, and in which the video signal is converted into a two-state detected signal as shown in Fig. 2. The operation of the device relies upon the fact that features of this type have asymmetrical boundary density profiles, i.e. when the scanning spot enters or leaves the boundary feature the resulting video signal has different emplitudes at equal intervals of time t (e.g. one picture element) on each side of the peak b, Fig. 2. In a first embodiment, Fig. 1, the video signal is fed through two delays 40 to form a first (t) and a second (2t) delayed video signal. The first delayed (t) video signal is released by gates 42 and 44 only when it is greater than the undelayed and second delayed video signals (logic units 48 and 46), i.e. the video signal from B only passes through gates 42 and 44 when the signal at B corresponds to a peak b. Two logic units 50 and 52 compare the signals at A and C to determine which is the greater and their outputs together with the signal from gate 44 are supplied to AND gates 54, 56, the outputs of which control a bi-stable circuit 58. When the signal amplitude at C is greater than that at A and the amplitude at B exceeds that at both A and C circuit 58 is " Set," and when the amplitude at A exceeds that at C and the amplitude at B exceeds that at both A and C circuit 58 is " Reset." In a second embodiment, Figs. 3 and 4, a ring having a thickness of one picture element is detected, five line scans each divided into five picture elements being shown. The input video signal is supplied to a delay matrix as shown in Fig. 3 which includes one scan line period delays 67 and picture element delays 69 and 40. The signals from the delays in advance of that from which the signal is supplied to gates 44 and 42 (as in Fig. 1) are weighted in accordance with their distances from b and added in circuit 71 to form an x signal and similarly the outputs from the following delays are added in circuit 72 to form a y signal. It can be shown mathematically that the sum of the picture elements to the right of the middle column of picture elements will always exceed the sum of those to the left of this column as the scanning spot enters the boundary feature whilst the reverse is so as the scanning spot leaves the boundary feature. Two comparison circuits 74 and 76 determine whether x or y is the greater and operate in conjunction with the detected boundary position to set and reset a bi-stable circuit 58 by means of AND gates 56 and 54 in the same way as in Fig. 1.