GB1237534A - Improvements in or relating to pattern recognition systems - Google Patents

Abstract

1,237,534. Pattern recognition. NATIONAL RESEARCH DEVELOPMENT CORP. 12 July, 1968 [11 July, 1967], No. 31941/67. Heading G4R. Pattern recognition apparatus transforms a position co-ordinate of the input pattern, or of an autocorrelation function of it, to a logarithmic scale and forms the autocorrelation function of the result to feed recognition means. Autocorrelation can be done: (a) using one or two transparencies of the pattern, by obtaining an optical image through both, or of the one through itself using a mirror (Specification 981,431 is referred to for variations), (b) the pattern can be stored on two charge storage meshes of an image storage tube and a flood of electrons passed through both to an output phosphor, (c) by an electrical network fed by a matrix of photo-cells, (d) by inserting the binarized outputs of a matrix of photo-cells in parallel into each of two shift registers, the second of which is then progressively shifted, each stage of one register being ANDed with the corresponding stage of the other to feed a respective counter, (e) by serializing the binarized outputs of a photo-cell matrix and shifting them into a shift register, each stage except the first of which feeds a respective counter via an AND gate controlled by the first stage, (f) as (e) except that the shift register input comes from a television-type scanner, (g) using tapped delay lines in place of a shift register, but using digital or analogue signals, (h) using a computer. The first autocorrelation, if used, may be partial, permitting detection of particular character features, e.g. vertical, horizontal and oblique straight lines and curves. These features could be cross-correlated before the logging. Logging can be done in the optical case by optical fibres, each going from a position in an input plane to the log of this position in an output plane. The log of the position with polar co-ordinates (r, #) is taken to be the position with rectangular cartesian co-ordinates (log r, #). Alternatively, distorting optical systems or the electron optical equivalent can be used for the logging, or a computer, or in the case of a television type scanner, scan conversion tubes can be used. The logged function may be exponentially weighted using an optical filter, or transformed to its second differential with respect to log r. Intensities are normalized before or after the logging. Recognition can be by use of an optical mask or masks, or an analogous electrical network. The autocorrelations, normalization and logging compensate for non-standard size, mispositioning and rotation of the pattern. If the output is required to be independent of size or rotation only, the second autocorrelation is performed in the log r or # direction only, respectively. Alternatively, the second autocorrelation may be complete in the log r direction and only partial in the # direction, giving independence of size and small rotations. The first autocorrelation is omitted if there can be no mispositioning of the input pattern.