Reference marker/correlation scheme for optical measurements

摘要

An optical measurement technique enables optical signal processing apparatus to eliminate the effects of environmental noise during scanning of a workpiece, wherein successive optical slices through the workpiece are obtained. The image samples derived by the scanning optics may not properly line up with one another, where there is relative vibrational motion between the workpiece and the scanning optics. To overcome this problem a reference marker/correlation scheme effectively aligns each of the picture slices of the workpiece relative to a stored reference marker by correlation, so that the composite of the adjacent samples of the stem accurately represents a picture of the workpiece.