Method and apparatus for discriminating in-focus images from out- of- focus light signals from background and foreground light sources

摘要

A method and apparatus for discriminating an in-focus image from an out-of-focus image which may be implemented in accordance with either or both an illumination procedure and a signal detection procedure includes collimating light rays emanating from a point in an object plane in an object to produce collimated rays. The collimated rays are focused onto a spot in an in-focus image plane. Light impinging on the spot is detected to measure the intensity thereof. The phase of a first portion of the collimated rays is shifted to produce a first quantity of phase- shifted rays, and the phase of a second portion of the collimated rays also is shifted to produce a second quantity of phase-shifted rays. The first and second quantities of phase-shifted rays are focused onto the spot. Light including the remaining non-phase-shifted rays and the first and second quantities of phase-shifted rays impinging on the spot is detected to measure the intensity thereof. The intensities measured for the remaining non-phase-shifted rays and the first and second quantities of phase- shifted rays are subtracted from the intensities measured for the rays focused on the spot in the in-focus image plane to cancel the effects of light from the out-of-focus image impinging on the spot to obtain an accurate representation of the object at the point in the object plane.