Patent ID: 7515280

Claim:
An apparatus for determining a high resolution surface displacement measurement relative to a target surface, the apparatus comprising: a light source arranged to project a beam of light onto the target surface; a detector arranged to receive light reflected from the target surface and configured to provide image data corresponding to the received light, wherein the detector has a number of pixels at least about 50% larger than a largest number of pixels that are included in a pixel address window that defines image data that is used by the apparatus for determining the high resolution surface displacement measurement; signal generating and processing circuitry operable to determine the high resolution surface displacement measurement, the signal generating and processing circuitry including a controller configured to determine the pixel address window and a memory including a pixel address window definition portion, wherein: the controller is configured to determine the pixel address window such that the pixel address window consists of a subset of pixels on the detector which have the best or sufficient image intensity and uniformity characteristics; the signal generating and processing circuitry is configured to determine a pixel correlation area that has an area smaller than the pixel address window, and which defines a number of pixel elements that will overlap in two successive correlation images and participate in correlation calculations used determine the high resolution surface displacement measurement; and the signal generating and processing circuitry is configured to determine the high resolution surface displacement measurement based on the pixel correlation area and the image data defined by the pixel address window.