Patent ID: 8194942

Claim:
An authentication apparatus comprising: a light source that emits an infrared light beam onto a finger; image pick-up means that picks up an image of the finger by using a transmitted light beam, and thus outputs an image signal; low-frequency brightness component extracting means that extracts a low-frequency brightness component signal from the image signal by using a low-pass filter; middle-frequency brightness component extracting means that extracts a middle-frequency brightness component signal from the image signal by using a middle-pass filter; correction means that corrects the middle-frequency brightness component signal by using the low-frequency brightness component signal; quaternary-value converting means that converts the corrected middle-frequency brightness component signal into quaternary values such that the quaternary values are distributed at a predetermined ratio; storage means that stores a quaternary-valued image obtained from the quaternary-value conversion by the quaternary-value converting means; correlation coefficient calculating means that calculates a correlation coefficient between a quaternary-valued evaluation image as an object of evaluation and a quaternary-valued registered image by using a pattern matching method based on a normalized correlation method, the quaternary-valued evaluation image obtained from the quaternary-value conversion by the quaternary-value converting means, the quaternary-valued registered image being beforehand stored in the storage means; and judgment means that judges whether or not the quaternary-valued evaluation image and the quaternary-valued registered image are images picked up from the same finger on a basis of the correlation coefficient which is calculated by the correlation coefficient calculating means.