1. Field of the Invention
This invention relates to a fingerprint characteristic extraction apparatus, and more particularly to a fingerprint characteristic extraction apparatus which extracts characteristics of a fingerprint to be used for classification and verification of the fingerprint as well as a fingerprint classification apparatus and a fingerprint verification apparatus for use with the fingerprint characteristic extraction apparatus.
2. Description of the Related Art
Various fingerprint identification apparatus wherein an inputted fingerprint pattern is searched out and identified from within a large number of fingerprint patterns registered in a data base are known, and a well known one of the fingerprint identification apparatus identifies a fingerprint pattern making use of characteristic points of the fingerprint. A fingerprint identification apparatus of the type just mentioned is disclosed, for example, in Japanese Patent Publication Application No. Showa 63-13226 or 63-34508.
It is examined here to effect, using such a fingerprint identification apparatus as described above, identification to detect regarding a search fingerprint card (hereinafter referred to as search side card) having fingerprint impressions for the 10 fingers collected from a certain person whether or not M registered fingerprint cards (hereinafter referred to as file side cards) include a search fingerprint card having fingerprint impressions for the 10 fingers collected from the same person on another opportunity.
In practical use, identification based on a plurality of fingers is performed in order to assure a higher degree of identification accuracy. Since the number of file side cards is large, in order to assure high speed processing of the file side cards, another apparatus has been proposed wherein characteristics of general patterns of fingerprints are extracted from images of fingers of a search side card and file side cards and compared with each other to select those file side cards which have similar characteristics to those of the search side card and verification processing is performed with the selected file side cards while those file side cards which are not similar are determined that they do not coincide with the search side card and the verification processing is not performed for them. It is to be noted that, of the processing operations mentioned, the processing operation for determination of whether the fingerprints of the search side card and a file side card have sufficient approximation to be subject to verification processing is called classification processing, and the processing operation for selective determination of a group of cards for which verification processing should be performed from among the file side cards is called preselection processing.
Characteristics of patterns used for such preselection processing are classified, according to a classification method (main classification), into three large general groups of patterns of loop, whorl and arch based on a general pattern shape of a ridge pattern and a positional relationship of characteristic points. This method is disclosed, for example, in Osamu Nakamura, "Fingerprint Classification by Directional Distribution Patterns", The Journal of Treatises of the Electronic Communications Society of Japan, Vol. J65-D, No. 10, October, 1982, pp.1,286-1,293, Shinichiro Itoh et al., "An Algorithm for Classification of Fingerprints Based on the Core", the Transactions of the Institute of Electronics, Information, and Communication Engineers of Japan D-II, Vol. J73-D-II, NO. 10, October, 1990, pp.1,733-1,741 or "The Science of Fingerprints", U.S. Department of Justice, Federal Bureau of Investigation. Further, in order to effect further accurate preselection processing, a further method is available wherein, as disclosed in "The Science of Fingerprints", patterns are classified based on a combination of information which includes not only main classification information of each finger but also sub information such as a distance between singular points (a core point and a delta point) on the fingerprint, a ridge count and so forth.
In the classification and preselection processing wherein a fingerprint pattern having characteristics similar to those of a particular fingerprint pattern is searched from among a large number of registered fingerprint patterns, it is desirable to extract a number of characteristics as large as possible from a fingerprint image and utilize a characteristic space as wide as possible in order to achieve a higher classification performance.