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Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.


Papers
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Patent
David R. Miers1
30 Jul 1996
TL;DR: In this article, a beam shaping aperture is inserted between the spatial filter and the focussing lens to shape the laser beam, which is a rectangular aperture having a height to width ratio in a range of from 3:1 to 5:1 such that each dimension is on the order of hundreds of micrometers.
Abstract: An optical illuminator assembly for an analytical instrument, such as a clinical hematology or a flow cytometer instrument, including a laser diode having a diverging laser beam output, a collimating lens to collimate the diverging laser beam, a spatial filter operating on the collimated laser beam to spatially filter the beam, and a focussing lens to focus the spatially filtered beam into a flow cell containing particles suspended in a moving stream. A beam shaping aperture is preferably inserted between the spatial filter and the focussing lens to shape the laser beam. The spatial filter preferably includes an objective lens, a collimating lens, and a filter aperture interposed between the objective and imaging lenses. The filter aperture is preferably rectangular, having a height to width ratio in the range of 1:2 to 1:3 such that each dimension is on the order of tens of micrometers. The beam shaping aperture is preferably a rectangular aperture having a height to width ratio in a range of from 3:1 to 5:1 such that each dimension is on the order of hundreds of micrometers.

86 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of speckle in partially coherent, monochromatic light is extended to cover the entire range of object roughness, and general relations are derived for the spatial correlation and the spatial Wiener spectrum.
Abstract: The theory of speckle in partially coherent, monochromatic light is extended to cover the entire range of object roughness. For “almost white-noise” objects it is shown how the speckle statistics are related to a Gaussian approximation of the object statistics. Within this approximation, general relations are derived for the spatial speckle correlation and the spatial Wiener spectrum. The theory is applied to calculate rms speckle contrast as function of object roughness, coherence of the illumination, and receiver plane defocusing.

86 citations

Journal ArticleDOI
TL;DR: It is shown that spatial low-pass filtering with a Gaussian filter can be used to reduce the effect of noise and recover useful signal if the noise is spatially incoherent and the Laplacian is effective when the spatial SNR is greater than 3.

86 citations

Journal ArticleDOI
TL;DR: A method to design lasers that emit an arbitrary beam profile is studied and a solid-state laser emitting beams with a two-dimensional Airy intensity profile is demonstrated both theoretically and experimentally.
Abstract: A method to design lasers that emit an arbitrary beam profile is studied. In these lasers, output-coupling is performed by a diffraction grating that imposes a phase and amplitude distribution onto the diffracted light. A solid-state laser emitting beams with a two-dimensional Airy intensity profile is demonstrated both theoretically and experimentally. In this case, the diffraction grating adds a transverse cubic phase to the diffracted light. An Airy beam is obtained by performing optical Fourier transform of the out-coupled light. The laser beam profile and power characteristics are shown to agree with theory.

86 citations

Patent
14 Aug 2001
TL;DR: In this paper, a motion compensated temporal filtering using previously generated motion vectors and adaptive spatial filtering at scene change frames is proposed to reduce the noise in a video system by applying motion compensation and adaptive spatio-temporal filtering.
Abstract: Noise is reduced in a video system by applying motion compensated temporal filtering using previously generated motion vectors and adaptive spatial filtering at scene change frames. Various types of noise can be introduced into video prior to compression and transmission. Artifacts arise from recording and signal manipulation, terrestrial or orbital communications, or during decoding. Noise introduced prior to image compression interferes with performance and subsequently impairs system performance. While filtering generally reduces noise in a video image, it can also reduce edge definition leading to loss of focus. Filtering can also tax system throughput, since increased computational complexity often results from filtering schemes. Furthermore, the movement of objects within frames, as defined by groups of pixels, complicates the noise reduction process by adding additional complexity. In addition to improvements made to FIR spatial filtering, the present invention improves on previous filtering techniques by using Infinite Impulse Response (IIR) temporal filtering to reduce noise while maintaining edge definition. It also uses motion vectors previously calculated as part of the first-pass image encoding or alternatively by transcoding to reduce computational complexity for P-frame and B-frame image preprocessing. Single stage P-frame temporal noise filtering and double stage B-frame temporal noise filtering are presented.

86 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202321
202265
202181
2020144
2019180
2018179