3,798 research outputs found
Extinction controlled adaptive phase-mask coronagraph
Context. Phase-mask coronagraphy is advantageous in terms of inner working
angle and discovery space. It is however still plagued by drawbacks such as
sensitivity to tip-tilt errors and chromatism. A nulling stellar coronagraph
based on the adaptive phase-mask concept using polarization interferometry is
presented in this paper. Aims. Our concept aims at dynamically and
achromatically optimizing the nulling efficiency of the coronagraph, making it
more immune to fast low-order aberrations (tip-tilt errors, focus, ...).
Methods. We performed numerical simulations to demonstrate the value of the
proposed method. The active control system will correct for the detrimental
effects of image instabilities on the destructive interference. The mask
adaptability both in size, phase and amplitude also compensates for
manufacturing errors of the mask itself, and potentially for chromatic effects.
Liquid-crystal properties are used to provide variable transmission of an
annulus around the phase mask, but also to achieve the achromatic {\pi} phase
shift in the core of the PSF by rotating the polarization by 180 degrees.
Results. We developed a new concept and showed its practical advantages using
numerical simulations. This new adaptive implementation of the phase-mask
coronagraph could advantageously be used on current and next-generation
adaptive optics systems, enabling small inner working angles without
compromising contrast.Comment: 7 pages, 6 figure
Hyperpixels: Flexible 4D over-segmentation for dense and sparse light fields
4D Light Field (LF) imaging, since it conveys both spatial and angular scene information, can facilitate computer vision tasks and generate immersive experiences for end-users. A key challenge in 4D LF imaging is to flexibly and adaptively represent the included spatio-angular information to facilitate subsequent computer vision applications. Recently, image over-segmentation into homogenous regions with perceptually meaningful information has been exploited to represent 4D LFs. However, existing methods assume densely sampled LFs and do not adequately deal with sparse LFs with large occlusions. Furthermore, the spatio-angular LF cues are not fully exploited in the existing methods. In this paper, the concept of hyperpixels is defined and a flexible, automatic, and adaptive representation
for both dense and sparse 4D LFs is proposed. Initially, disparity maps are estimated for all views to enhance over-segmentation accuracy and consistency. Afterwards, a modified weighted K-means clustering using robust spatio-angular features is performed in 4D Euclidean space. Experimental results on several dense and sparse 4D LF datasets show competitive and outperforming performance in terms of over-segmentation accuracy, shape regularity and view consistency against state-of-the-art methods.info:eu-repo/semantics/publishedVersio
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