Minimum Resolvable Contrast Measurement Device for Video Systems

摘要

This invention is directed to an apparatus for generating optical images having backgrounds of uniform and constant luminance with a nonperiodic, variable contrast pattern superimposed thereon. Two controllable intensity beams of uniform luminance are projected to a focus at the image plane. One of the beams contains a nonperiodic opaque pattern. Each beam passes through a linear polarizer, which polarizers are orthogonally oriented relative to each other. After beam splitting and interlacing, one of the two output beams formed is projected through a rotatable linear polarizer and onto an optical sensor at the image plane. The second split and interlaced beam is projected through a synchronized, rotatable linear polarizer, and then onto a detector assembly for measuring both background intensity and pattern contrast levels. Variations in the background intensity are sensed in the detector assembly, decoupled according to polarization and apportioned according to polarization as feedback signals to correct for drift in each of the two beam sources. Rotation of the polarizer in the optical path leading to the optical sensor changes the photometric luminance of the non-periodic pattern without altering the background luminance level.