Abstract
In certain imaging applications, conventional lens technology is constrained by the lack of materials which can effectively focus the radiation within a reasonable weight and volume. One solution is to use coded apertures—opaque plates perforated with multiple pinhole-like openings. If the openings are arranged in an appropriate pattern, then the images can be decoded and a clear image computed. Recently, computational imaging and the search for a means of producing programmable software-defined optics have revived interest in coded apertures. The former state-of-the-art masks, modified uniformly redundant arrays (MURAs), are effective for compact objects against uniform backgrounds, but have substantial drawbacks for extended scenes: (1) MURAs present an inherently ill-posed inversion problem that is unmanageable for large images, and (2) they are susceptible to diffraction: a diffracted MURA is no longer a MURA. We present a new class of coded apertures, separable Doubly-Toeplitz masks, which are efficiently decodable even for very large images—orders of magnitude faster than MURAs, and which remain decodable when diffracted. We implemented the masks using programmable spatial-light-modulators. Imaging experiments confirmed the effectiveness of separable Doubly-Toeplitz masks—images collected in natural light of extended outdoor scenes are rendered clearly.
Highlights
Coded-aperture imaging was introduced by Dicke[1] and Ables[2] in the 1960s, and the field developed rapidly for astronomical x-ray and gamma-ray imaging
To address the ill-posed imaging problem, we developed a new class of coded aperture masks which provide compelling advantages over modified uniformly redundant arrays (URAs) (MURAs)
Our goal was to improve the performance of completely lensless imagers, especially for imaging extended scenes in natural light
Summary
Coded-aperture imaging was introduced by Dicke[1] and Ables[2] in the 1960s, and the field developed rapidly for astronomical x-ray and gamma-ray imaging. Coded-aperture imagers extend the pinhole camera concept, which requires no lenses, has unlimited depth of focus, and can image radiation of any wavelength. By placing a large number of pinholes in a common aperture plane, the light-gathering capability is greatly increased. Improved sensitivity comes at the price of having the focal plane record a multiplex of overlapping images, requiring algorithmic reconstruction to render a clear image. Coded-aperture imaging is a subset of the general field of computational imaging. By placing the pinholes in prime-number-based patterns determined by sampling theory, it was thought that the near-delta-function system point-spread functions (PSFs) could be achieved (after deconvolving the distribution with appropriate filter functions), greatly improving the image reconstruction
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