Method and apparatus for discriminating ambient light in a fingerprint scanner
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United States of America Patent
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Issued Date -
Nov 10, 2005
app pub date -
Apr 29, 2005
filing date -
Apr 29, 2004
priority date (Note) -
Abandoned
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Abstract
A surface pattern imaging device applicable to fingerprint and other surface imaging applications operates with an illumination source. In an embodiment, the illumination source is a narrow band green light, and an optical imaging path of the reader includes a green band pass filter and an infrared (IR) cutoff filter between the surface of interest and an image sensor. The filters prevent ambient light outside the green range from reaching the image sensor. In an exemplary embodiment useful in fingerprint imaging, ambient light wavelengths in the green range are absorbed and blocked naturally by the finger, and therefore cannot pass through the finger into the imaging path. Ambient light in other ranges, particularly including the red and infrared ranges which may pass through the finger, is attenuated by the band pass and IR cutoff filters. The image sensor in the improved reader therefore receives the light reflected from the green illumination source, while interference from ambient light sources is substantially attenuated.
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