Topic
Spatial filter
About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.
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TL;DR: The purpose of this note is to show an experimental verification of Mertz' idea, and to comment on the usefulness of this zoom effect.
Abstract: Holograms of spatially incoherent objects can be made with an interferometer which divides the light from each point into two partial waves and recombines them in the hologram plane to form interference fringes. By moving or rotating certain com ponents of the interferometer, the scale of the fringes can be varied. This changes the magnification of the reconstructed image, as Mertz has pointed out, giving a zoom capability without any additional components. The purpose of this note is to show an experimental verification of Mertz' idea, and to comment on the usefulness of this zoom effect. In our experiments we used a triangular path interferometer with radial shear, and a Mach-Zehnder interferometer with variable rotational shear. Figures 1 and 2 show the experi mental arrangements. The object is placed in the front focal plane of a lens with focal length f. An object point having posi tion vector χ will create a plane wave of amplitude
34 citations
TL;DR: In this article, a general theory of optical-aberration tests, encompassing many well-known practical tests, is presented, utilizing the formalism of spatial filtering, employing coherent illumination.
Abstract: A general theory of optical-aberration tests, encompassing many well-known practical tests, is presented, utilizing the formalism of spatial filtering, employing coherent illumination. The basic diffraction integrals of the Ronchi-grating test, Foucault knife-edge test, phase Foucault knife-edge test, and the Zernike phase-contrast test are derived. Typical situations have been analyzed and numerical results are shown and discussed.
34 citations
TL;DR: A novel spatial filtering method, called Double Layered-Background Removal Filter (DL-BRF), for achieving high detection rates and low false alarm rates is presented and the adaptive Hysteresis threshold-based scheme is a suitable detection method.
Abstract: Detecting small targets is essential for mitigating the sea-based Infrared search and track (IRST) problem. It is easy to detect small targets in homogeneous backgrounds such as the sky. When targets are on the border line of heterogeneous backgrounds such as the horizon in the sky and sea surface, solving the problem of detection becomes difficult. This paper presents a novel spatial filtering method, called Double Layered-Background Removal Filter (DL-BRF), for achieving high detection rates and low false alarm rates. DL-BRF consists of a Modified-Mean Subtraction Filter (M-MSF) and a consecutive Local-Directional Background Removal Filter (L-DBRF). M-MSF enhances the target signal and reduces background noise. L-DBRF removes horizontal structures, which upgrade the signal-to-clutter ratio and background suppression factor. L-DBRF used after M-MSF enhances the synergistic performance of horizontal target detection. Additionally, the adaptive Hysteresis threshold-based scheme is a suitable detection method. We validate the superior performance of the proposed method via three types of evaluation tests, including a real test scenario.
34 citations
TL;DR: These spatially dispersive modes of metasurfaces with an angle-dependent excitation can be used to directly manipulate the spatial frequency content of an incident field, suggesting their use as ultra-compact alternatives for analog optical information processing.
Abstract: Here we consider image processing using the optical modes of metasurfaces with an angle-dependent excitation. These spatially dispersive modes can be used to directly manipulate the spatial frequency content of an incident field, suggesting their use as ultra-compact alternatives for analog optical information processing. A general framework for describing the filtering process in terms of the optical transfer functions is provided. In the case where the relevant mode cannot be excited with a normally incident plane wave (a dark mode), high-pass filtering is obtained. We provide examples demonstrating filtering of both amplitude and pure phase objects.
34 citations
TL;DR: This paper replaces the variable diameter Fourier filter with a digital micromirror device (DMD) to extend the assessment of morphology to the characterization of particle shape and orientation and shows how this system can be used to assess particle aspect ratio even when imaged at low resolution.
Abstract: We had developed Optical Scatter Imaging (OSI) as a method which combines light scattering spectroscopy with microscopic imaging to probe local particle size in situ. Using a variable diameter iris as a Fourier spatial filter, the technique consisted of collecting images that encoded the intensity ratio of wide-to-narrow angle scatter at each pixel in the full field of view. In this paper, we replace the variable diameter Fourier filter with a digital micromirror device (DMD) to extend our assessment of morphology to the characterization of particle shape and orientation. We describe our setup in detail and demonstrate how to eliminate aberrations associated with the placement of the DMD in a conjugate Fourier plane of our microscopic imaging system. Using bacteria and polystyrene spheres, we show how this system can be used to assess particle aspect ratio even when imaged at low resolution. We also show the feasibility of detecting alterations in organelle aspect ratio in situ within living cells. This improved OSI system could be further developed to automate morphological quantification and sorting of non-spherical particles in situ.
34 citations