Contact screen and method for nonlinear transformations and filtering in coherent optical systems

摘要

Halftone contant screens, their manufacture and their use for performing nonlinear transformations and filtering over a large dynamic range in coherent optical image processing systems are described. The screens are effective for the removal or filtering of multiplicative signals and noise and may be made to provide logarithmic, exponential and square-law transformations as well as other nonlinear but not necessarily mathematically defined transformations depending on the specific application. Some of the possible specific applications include the removal of speckle noise in laser light imaging, extraction of images from multiplicative noise such as images of non-uniformly illuminated transparencies, and biomedical image processing.