Patent GB-1391056-A (GB)
Title: Feature parameter measurement by line scanning
IPC: G06T7/60
Filed: 1971-04-17
Abstract: 1391056 Image analysis IMAGE ANALYSING COMPUTERS Ltd 4 April 1972 [17 April 1971 21 Sept 1971] 9738/71 and 43912/71 Heading G4D [Also in Division G1] The vertically projected length V, Fig. 1, of a feature in a field, is determined by electronically scanning the field or an image thereof to generate a video signal which is compared with a reference voltage 11, Fig. 3, to generate a signal pulse whenever a comparison criterion is satisfied, this signal being delayed, at 40, by one line scan period and inverted, 44, before application to an AND gate 42 to which the next signal pulse is applied direct, so that a difference pulse is generated of duration equal to the parts of this next signal pulse which are not coincident with the delayed pulse, the difference pulses being accumulated at 45. The video signal at I for the five lines scans 1-5 of Fig. 1, is indicated at Fig. 4 (top) and the differences pulses at Fig. 4 (bottom). Accumulator 45 may simply be an integrator, or if a chopper 43 is provided, a counter. The circuit of Fig. 3 may constitute the computer module C, in Fig. 2, which comprises a coincidence circuit (11) and an associated parameter computer (rest of Fig. 2), as described in Specifications 1,264,804 and 1,264,805, in which case accumulator 45 is reset at the end of each modified video signal pulse. Summing of the difference pulses may be performed in computer module A where chopping is not performed in Fig. 3. If chopping at 43 is carried out, the number of pulses on each line scan in the output of C are counted, and digital information can be circulated in delay device 28, so that a parallel word may be issued through gate 36 when this is opened at the end of each feature. In order to identify the shapes of features, e.g. whether circular or elongated, for example, in the differentiation of silicate from alumina and/or oxide inclusions in steel the horizontally projected length H has also to be determined, the ratio of this to V being calculated, indicative of the shape. Counts of features of different shapes (different H/V ratios) may then be carried out. H is calculated by counting the number of line scans which intersect a feature, by the circuit of Fig. 5 or 6 (not shown). The ratio H/V is determined by the circuit of Fig. 7 (not shown), operating on digital signals delivered by the circuit of Fig. 2 at IV. A circuit arrangement for determining the perimeter of a feature is described, Fig. 8 (not shown), In this, two circuits (58, 60) detecting coincidence of leading and trailing edges, respectively, of features in consecutive scans are used to produce pulses representing the number of portions of the perimeter which are substantially perpendicular to the line scan Perimeter portions parallel to the line scan are determined by a circuit (62) equivalent to Fig. 3, but in which the undelayed path to the AND gate contains a chopper fed by clock pulses, and a circuit (64) which is the inverse of Fig. 3. The pulses from each of circuits 58-64 are counted and fed to a total counter. A less accurate measurement may be obtained by using only one each of circuits 58, 60 and 62, 64, and doubling the counts for each. A more accurate measurement may be obtained by use of further circuits 66, 68 by which can be added in an incremental count value (0À3) for each occasion that the difference between the leading edge co-ordinates on adjacent lines is less than the distance curved by the scanning spot in the line scan direction between gating or clock pulses. These circuits can utilize the leading and trailing edge detectors of circuits 58, 60. It may be desirable in some cases to width discriminate the signal pulses before formation of differences in the Fig. 3 circuit.