Patent GB-1240630-A (GB)
Title: A device for identifying a pattern
IPC: G06V10/20
Filed: 1969-09-03
Abstract: 1,240,630. Pattern recognition. C.I.T. COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 6 Sept., 1969 [4 Sept., 1968], No. 43686/69. Addition to 1,186,169. Heading G4R. A device for identifying a pattern, e.g. fingerprint, consisting of lines and points on the lines which are significant of the pattern, comprises a coder receiving the pattern and producing electrical signals, each representative of a point on the pattern, and circuitry for rejecting non-singular, non-characteristic and border points, calculating the slope of the tangent to the pattern line at each remaining point, selecting a group of a preselected number of characteristic points arranged in a predetermined order and calculating, from the tangent slopes and co-ordinates of the points, data significant of a closed figure with straight sides joining the points in the predetermined order, the data significant of at least one such figure of the unknown pattern being compared with data significant of such figures of known patterns, coincidence of the unknown pattern with a known pattern being indicated when a preselected number of such figures are common to the two patterns. The fingerprint is scanned in a repeated horizontal raster by a TV camera, the resulting video being thresholded then passed to a 3-bit shift register the stages of which feed a majority gate in parallel to halve the number of bits horizontally. Further shift registers feeding a second 3-input majority gate then halve the number of bits vertically. A processing memory, consisting of thirteen 15-bit shift registers, connected in series but with provision for recycling each register separately, receives the reduced data for successive windows in the scan field, one window at a time. Each window is 26 x 30 bits (before reduction). The scan field is divided into columns of windows, successive windows in a given column being two scan lines lower, and successive columns overlapping by half a column width. For each given point in the centre shift register of the processing memory in turn, the 8 surrounding points are placed in a ring shift register which is ring shifted so that logic can detect if the given point is singular (i.e. if between 4 and 7 of the surrounding points have the opposite binary value), the idea being to detect termini of print lines. The positions and values of singular points are stored in a set of five 8-bit shift registers. Which of the singular points are to be retained, at least provisionally, as characteristic, is decided by circuitry which, while the registers of the processing memory recycle, examines the centre shift register then those two adjacent to it in turn, then either the registers on one side of the central three or those on the other in turn, to follow the print line involving the singular point. The positions of the limits of the line in each register are stored during this. Logical conditions derived reject singular points as non-characteristic if it appears they are noise or unsuitable or not required for calculation of a tangent, and determine how the tangents are to be calculated. Tangent data and characteristic point co-ordinates are passed to a store via a buffer to provide the information for the closed figures referred to above, either relating to an unknown print to be recognized or known prints during a learning phase. However, this is not done with respect to points which are border points, i.e. of the whole print or of, e.g. a scar. A point (in the centre register of the processing memory) is recognized as a border point if the 6 registers above or below the centre register contain a 6 x 6 block of points of the same value. During insertion of another line of data into the processing memory, the values of 6 points forming a column in the registers above the centre register are sampled and if they are the same, a counter is incremented. If the next column of points have the same value as each other and the previous column, the counter is incremented again, otherwise it is reset. A count of 6 identifies a border point. Identical arrangements are provided to identify a border point in response to the 6 registers below the centre register.