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

[0008] According to the present invention, a mask for an optical imaging system is designed by optimizing an optical property (transmittance or reflectance) of the mask relative to the incident intensity distribution (rather than e.g. the incident optical field distribution) on the image plane of the optical imaging system. The mask then is fabricated in accordance with the optimized optical property. The mask overcomes misfocus degradation in the optical imaging system.

[0015] Preferably, the one- or two-dimensional mask is real, which means that the phase of the mask transmittance is either 0 or π. Fabrication of such a mask is eased, inasmuch as it requires the implementation of only two phases.

[0016] Preferably, the one- or two-dimensional mask is a phase-only mask. Doing without amplitude variations or absorbing portions on the mask simplifies fabrication and increases light throughput.

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.

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