Reflecting the increase in people's sense of security, use of a face recognition system has been rapidly expanding in recent years. The face recognition system has advantages that a conventional recognition system which uses a code number does not have. For example, the face recognition system has a significantly lower possibility that information (i.e., a characteristic of a person's face) necessary for recognition is stolen by others; and convenience such that recognition can surely be carried out as long as a person to be recognized is in the place. Because of these advantages, it is expected that the face recognition system will become further widespread.
Nevertheless, the face recognition system still has various kinds of problems unsolved. One of the problems is that its recognition accuracy is not sufficiently high yet. The face recognition system does not reach such a level that allows recognition merely by showing a face image. For example, such a problem actually occurs that a change in brightness of a person's background prevents recognition of the person.
In view of this, various kinds of techniques have been proposed so far for the purpose of improving accuracy of face recognition.
For example, Patent Document 1 discloses an image searching method including the steps of (i) detecting, from an image, frames containing face images; (ii) extracting the face images from the frames; (iii) grouping, out of all the face images thus extracted, the face images showing the same person to the same group; and (iv) extracting a representative face image for each person.
This method focuses on a face in an image in its detection process, and identifies the face thus detected. This makes it possible to display faces of persons shown in an image in such a manner that a face of a person is distinguished from a face of another person.
Patent Document 2 discloses a personal recognition device including: means for inputting, per frame, image data which is used for recognizing a person; means for detecting a face area from the image data; means for working out a characteristic amount in the face area; means for judging whether or not the characteristic amount is valid by comparing the characteristic amount with a standard value; means for storing characteristic amounts which are respectively worked out for a plurality of frames and are judged to be valid; means for obtaining a characteristic amount for face recognition by calculating the characteristic amounts respectively worked out for the plurality of frames; and means for recognizing the person by comparing the characteristic amount for recognition with a prestored face characteristic amount.
This device prevents a decrease in recognition accuracy even when a head posture or the expression of a face changes. This improves accuracy in working-out of a characteristic amount used for judging a valid frame.
Patent Document 3 discloses a recognition system including: a face recognition database for storing a plurality of pieces of face information which are obtained by capturing, in a plurality of different circumstances, a face image of a person to be recognized and each of which pieces of face information has a pattern name corresponding to each of the circumstances; a person-to-be-recognized identification table for associating a certain pattern name stored in the face recognition database with the person to be recognized whose image is captured under the certain pattern name; a camera for obtaining the face information by capturing the face image of the person to be recognized; recognition processing means for comparing the face information captured by the camera with the plurality of pieces of face information stored in the face recognition database so as to determine face information having the highest similarity; person-to-be-recognized identification means for identifying, by looking up the pattern name in the person-to-be-recognized identification table, the person who is to be recognized and corresponds to the pattern name of the face information determined by the recognition processing means.
This system prepares a plurality of pieces of face information obtained in different circumstances. This makes it possible to recognize a face in any circumstances.
Patent Document 4 discloses a device for adding a new entry to a face-image database which device registers a new person in a personal-face-image database and a personal-face-feature database. The device disclosed in Patent Document 4 includes: estimation means for estimating (i) the positions of a plurality of characteristic points in a face area of a person shown in an inputted image and (ii) the direction of a face of the person; selection means for selecting, from the inputted image, a frame in which the face of the person points a predetermined direction, the selection being made in accordance with information on the direction of the face estimated by the estimation means or information on the direction of the face which is externally inputted; user interface means for causing to display, in response to a command given by a user, (i) the frame selected by the selection means and (ii) information relevant to the frame; working-out means for working out, in the vicinity of the plurality of characteristic points estimated by the estimation means, a characteristic amount of the face of the person in the frame selected by the selection means so as to obtain a database component of the person shown in the inputted image.
This device makes it possible to automatically register a new person in a database.
[Patent Document 1]
    Japanese Unexamined Patent Application Publication, Tokukai, No. 2001-167110 (published on Jun. 22, 2001)[Patent Document 2]    Japanese Unexamined Patent Application Publication, Tokukaihei, No. 6-259534 (published on Sep. 16, 1994)[Patent Document 3]    Japanese Unexamined Patent Application Publication, Tokukai, No. 2005-115481 (published on Apr. 28, 2005)[Patent Document 4]    Japanese Unexamined Patent Application Publication, Tokukai, No. 2002-133423 (published on May 10, 2002)