Patent ID: 7310434

Claim:
A fingerprint authentication apparatus for processing image signals of a finger read out from a sensor containing a plurality of photoelectric converters arrayed two dimensionally and producing first, second, and third image signals of a plurality of lines of pixels comprising first and second sets of lines of pixels that are different from each other, the apparatus comprising: a low-pass filter receiving the first set of lines of the first image signal of the finger and being configured: to remove the portion of the first set of lines of the image signal representing fingerprint ridges; and to transmit therethrough a shading-noise signal component of the first set of lines of the image signal comprising: dark shading noise comprising photoelectric converter noise and/or unevenness in the dark output of the photoelectric converters with respect to a reference level, and/or light-shading noise comprising uneven-lighting noise resulting from unevenness in the luminance of the image signals due to the form and reflectivity of the finger, a light source illuminating the finger, an optical system imaging an image of the finger, and/or unevenness in the sensitivity of the photoelectric converters to light reflected by the finger, the low-pass filter being configured to extract from the first set of lines of the first image signal of the finger obtained by the sensor, the shading-noise signal component having a frequency range lower than a predetermined frequency, the predetermined frequency being lower than a frequency capable of expressing fingerprint ridges; a shading data generator configured to receive the shading-noise signal component of the first set of lines of the first image signal, and to generate, by interpolating between the first set of lines of the extracted shading-noise signal component of the first image signal of the finger, a shading-noise signal component of the second set of lines of the second image signal of the finger comprising: dark shading noise comprising photoelectric converter noise and/or unevenness in the dark output of the photoelectric converters with respect to a reference level; and/or light-shading noise comprising uneven-lighting noise resulting from unevenness in the luminance of the image signals due to the form and reflectivity of the finger, a light source illuminating the finger, an optical system imaging an image of the finger, and/or unevenness in the sensitivity of the photoelectric converters to light reflected by the finger; a removing unit configured to subtract from the third image signal of the finger obtained by the sensor not having passed through the low-pass filter or the shading data generator, the shading-noise signal component of the second set of lines of the second image signal generated by said shading data generator, and to output a difference image signal; and a verification unit configured to match the difference image signal output from said removing unit with a pre-stored image signal.