Importance

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Abstract

A method and device for acquiring data related to topography of a medium includes projecting light, allowably from more than one direction, onto the surface of the medium at an angle of less than sixteen degrees relative to the surface and imaging the surface. For example, the imaging sensor may be an array of sensor elements that is used to determine navigation of a hand-held scanner along an original. By introducing light at an angle of less than sixteen degrees, surface irregularities cast shadows that form a high contrast illumination pattern along the surface of the medium. The navigation sensor detects multi-element variations of intensity of scattered light from the surface with respect to positions along the surface, so that the Nyquist criteria are adequately satisfied. Typically, the light is collimated incoherent light, but this is not critical. The illumination angle can be established by using a prism. The prism may have an antireflective thin film coating on one or more prism faces. The employment of a prism provides a number of advantages, such as use of a transparent surface in contact with the media and raising the illumination source(s) away from the media.

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First Claim