Apparatus and method for improving contrast detected in a fringe projection autofocus system

摘要

A method and apparatus are provided, for improving contrast detected in a fringe projection autofocus system that projects light from a substrate to a digital camera. The method and apparatus reduce the fill factor of the digital camera in a direction that improves the contrast at spatial frequencies near or above the Nyquist limit in that direction.

主权项

1. A method for improving contrast in a fringe projection autofocus system, the method comprising:
scanning the substrate in a direction of a scan; forming an image of a fringe pattern, formed by a fringe projection portion of the fringe projection autofocus system on a substrate, at a surface of a digital camera by projecting light reflected from the substrate in a direction that is oblique with respect to the substrate,
wherein said fringe pattern is spatially-periodic at least in a first direction, and said image being spatially-periodic at least in a second direction; reducing a fill factor of the digital camera in a chosen direction defined such as to improve the contrast at spatial frequencies near and above the Nyquist limit in the chosen direction, wherein said reducing includes reducing the fill factor in the direction of a scan while substantially maintaining the fill factor a direction transverse to the direction of a scan.