| 摘要 |
1,198,984. Character recognition. HAWKER SIDDELEY DYNAMICS Ltd. 19 July, 1967 [21 July, 1966], No. 32904/66. Heading G4R. [Also in Division G2] In amethod of recognizing images or characters, each subject to be recognized, constituting one of a set of known subjects, has its diffraction pattern thrown on to a matched holographic filter for each of the known subjects, the filter for any known subject having been modified in manufacture by means of information relating to the other known subjects so as to cause the filter to reject the other subjects at least to some extent. As described, the holographic filter for a given subject is obtained by prefogging a photographic film or plate to get it on to the linear part of the transmissivity/ exposure curve, then exposing it for a time T to the given subject and a reference beam to produce a Fourier-transform hologram, then exposing it in turn to the other subjects in a similar way. In the cases of the other subjects the exposure times (expressed as a ratio with T) and the relative phases of the subject-illuminating beam and the reference beam (the same as with the given subject or 180 degrees different) are chosen so that the final filter obtained after development gives maximum discrimination between the given subject on the one hand and other subjects on the other. Equations indicating the required exposure ratios and relative phases in terms of the auto and crosscorrelation functions between the subjects (which may be calculated or measured) are given. T is chosen so that the total exposure does not take the plate or film off the linear range.
|
