Optical mask for all-optical extended depth-of-field for imaging systems under incoherent illumination

Abstract

A mask for enhancing the depth of focus of an optical imaging system is designed by optimizing an optical property (transmittance or reflectance) of the mask relative to the intensity distribution in the system's image plane. Preferably, a desired PSF intensity is selected, a desired misfocus parameter range is selected, and the optical property is adjusted to minimize a measure of the departure of the system's PSF intensity, as computed from the mask's optical property, from the desired PSF intensity, over the entire misfocus parameter range. Most preferably, the desired PSF intensity is selected as the inverse Fourier transform of a desired OTF. Preferably, the mask is fabricated as a DOE.

Description

FIELD AND BACKGROUND OF THE INVENTION [0001] The present invention relates to optical imaging and, more particularly, to a mask for insertion in the pupil of an optical imaging system that provides extended depth of field for imaging scenes located in the extended depth of field region and illuminated by incoherent light without needing to process the image created by the imaging system that incorporates the mask. [0002] Imaging systems are known to require accurate focus alignment. Conventional imaging systems, for example cameras, are very sensitive to misfocus. When the object and image planes are not in conjugate positions, the resultant image is severely degraded. Nevertheless, there are many applications (e.g. barcode reading, computer or machine vision, surveillance cameras, etc.) that require imaging of objects located anywhere within an extended depth of field (DOF) region, while allowing reduced contrast and resolution. [0003] Conventional solutions for imaging systems wit...

AI Technical Summary

Benefits of technology

The present invention provides a mechanism for improving the optical performance of an imaging system by designing a mask that optimizes its optical properties relative to the incident intensity distribution on the image plane of the system. The mask can be inserted in the optical path of the system or applied to existing optical elements. The mask is designed to overcome misfocus degradation in the system and can be fabricated using existing methods such as etching, injection molding, deposition, or casting. The optical element or system that includes the mask has improved optical performance and can be used in various applications such as lenses, filters, windows, and surveillance security imaging systems.

Problems solved by technology

When the object and image planes are not in conjugate positions, the resultant image is severely degraded.

The main disadvantages with such solutions are reduced resolution and low light throughput.

Nevertheless, the intermediate image is insensitive to misfocus for a wide range of DOF.

Practically, resolution is limited by CCD pixel size, as well as by the presence of noise, which may even be amplified in the processing stage.

Images