Spatial filter

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

Circular harmonic phase filters for efficient rotation-invariant pattern recognition

Abstract: A generalized approach for pattern recognition using spatial filters with reduced tolerance requirements was described in some recent publications. This approach leads to various possible implementations such as the composite matched filter, the circular harmonic matched filter, or the composite circular harmonic matched filter. The present work describes new examples leading to very high selectivity filters retaining rotation invariance and reduced requirements on device resolution. Computer simulations and laboratory experiments show the advantages of this approach.

Directional support value of Gaussian transformation for infrared small target detection.

Abstract: Robust small target detection is one of the key techniques in IR search and tracking systems for self-defense or attacks. In this paper we present a robust solution for small target detection in a single IR image. The key ideas of the proposed method are to use the directional support value of Gaussian transform (DSVoGT) to enhance the targets, and use the multiscale representation provided by DSVoGT to reduce the false alarm rate. The original image is decomposed into sub-bands in different orientations by convolving the image with the directional support value filters, which are deduced from the weighted mapped least-squares–support vector machines (LS–SVMs). Based on the sub-band images, a support value of Gaussian matrix is constructed, and the trace of this matrix is then defined as the target measure. The corresponding multiscale correlations of the target measures are computed for enhancing target signal while suppressing the background clutter. We demonstrate the advantages of the proposed method on real IR images and compare the results against those obtained from standard detection approaches, including the top-hat filter, max–mean filter, max–median filter, min–local–Laplacian of Gaussian (LoG) filter, as well as LS–SVM. The experimental results on various cluttered background images show that the proposed method outperforms other detectors.

Spatial filtering surface operative with antenna aperture for modifying aperture electric field

Abstract: A spatial filtering surface (100) includes a dielectric substrate (106) and a plurality of spaced, geometrically configured, resonant elements (104) positioned on the dielectric substrate (106). The resonant elements (104) form concentric rings that each attenuate any electromagnetic radiation passing therethrough a different amount wherein a spatial filter transform is imparted for tapering the magnitude and phase of a produced aperture field.

Efficient method for controlling the spatial coherence of a laser

Abstract: An efficient method to tune the spatial coherence of a degenerate laser over a broad range with minimum variation in the total output power is presented. It is based on varying the diameter of a spatial filter inside the laser cavity. The number of lasing modes supported by the degenerate laser can be controlled from 1 to 320,000, with less than a 50% change in the total output power. We show that a degenerate laser designed for low spatial coherence can be used as an illumination source for speckle-free microscopy that is nine orders of magnitude brighter than conventional thermal light.

Compact Scheme with Filtering for Large-Eddy Simulation of Transitional Boundary Layer

Abstract: Bypass transition induced by freestream turbulence is numerically simulated by compressible large-eddy simulation and implicit large-eddy simulation using a compact differencing scheme with spatial filtering. Simulated transitional flowfields qualitatively reproduce the physics of the transition and are appropriate for the discussion of transitional flowfields. Key coherent structures, such as low-speed streaks, longitudinal vortex pairs, and hairpin vortices, which play important roles in determining the behavior of transition, need to be directly resolved to properly simulate the physics of transition. Only a slight numerical damping of these coherent structures by the spatial filtering procedure causes the delay of transition. On the other hand, once the flow develops into a fully turbulent state, the spatial filtering has little influence on the flowfield. At the late stage of transition, the coherent structures break down into finer scales which require finer grid resolution to accurately resolve. However, the underresolution of the finer scale structures has little influence on the overall results if the key coherent structures are adequately resolved. Under the condition examined, the tenth-order filtering with α f = 0.495 does not act as an implicit subgrid-scale model. The present results reasonably illustrate the capability of compact/filter-based compressible large-eddy simulation and the guidelines regarding how to properly simulate transitional boundary layers using the large-eddy simulation.