Patent ID: 8077929

Claim:
A fingerprint reader, comprising: an illumination source that produces light; a camera; an optical window; an ambient light filter in contact with the optical window; wherein the light from the illumination source enters the optical window at a total internal reflection angle, such that the light is reflected off a surface of the optical window by total internal reflection; wherein when a person's finger is placed on the optical window, the light from the illumination source is frustrated by oils on ridges of the finger and is not reflected off the optical window; wherein the filter allows the light from the illumination source to pass through the filter at the total internal reflection angle inside the optical window while reflecting ambient light coming from outside of the optical window so that the ambient light does not reach the camera; wherein the ambient light can cancel or diminish the quality of a desired fingerprint to be imaged; wherein the illumination source and the filter are designed so that the light from the illumination source contacts the filter within a desired range of angles, so that the light from the illumination source is not affected by the filter; and wherein the filter is designed so that the ambient light contacts the filter outside of the desired range of angles, so that the filter rejects the ambient light.