167 research outputs found
Domain-Size Pooling in Local Descriptors: DSP-SIFT
We introduce a simple modification of local image descriptors, such as SIFT,
based on pooling gradient orientations across different domain sizes, in
addition to spatial locations. The resulting descriptor, which we call
DSP-SIFT, outperforms other methods in wide-baseline matching benchmarks,
including those based on convolutional neural networks, despite having the same
dimension of SIFT and requiring no training.Comment: Extended version of the CVPR 2015 paper. Technical Report UCLA CSD
14002
Sparse Modeling for Image and Vision Processing
In recent years, a large amount of multi-disciplinary research has been
conducted on sparse models and their applications. In statistics and machine
learning, the sparsity principle is used to perform model selection---that is,
automatically selecting a simple model among a large collection of them. In
signal processing, sparse coding consists of representing data with linear
combinations of a few dictionary elements. Subsequently, the corresponding
tools have been widely adopted by several scientific communities such as
neuroscience, bioinformatics, or computer vision. The goal of this monograph is
to offer a self-contained view of sparse modeling for visual recognition and
image processing. More specifically, we focus on applications where the
dictionary is learned and adapted to data, yielding a compact representation
that has been successful in various contexts.Comment: 205 pages, to appear in Foundations and Trends in Computer Graphics
and Visio
Introduction to the absolute brightness and number statistics in spontaneous parametric down-conversion
As a tutorial, we examine the absolute brightness and number statistics of photon pairs generated in spontaneous parametric down-conversion (SPDC) from first principles. In doing so, we demonstrate how the diverse implementations of SPDC can be understood through a single common framework, and use this to derive straightforward formulas for the biphoton generation rate (pairs per second) in a variety of different circumstances. In particular, we consider the common cases of both collimated and focused Gaussian pump beams in a bulk nonlinear crystal, as well as in nonlinear waveguides and micro-ring resonators. Furthermore, we examine the number statistics of down-converted light using a non-perturbative approximation (the multi-mode squeezed vacuum), to provide quantitative formulas for the relative likelihood of multi-pair production events, and explore how the quantum state of the pump affects the subsequent statistics of the down-converted light. Following this, we consider the limits of the undepleted pump approximation, and conclude by performing experiments to test the effectiveness of our theoretical predictions for the biphoton generation rate in a variety of different sources
Interferometric Imaging Directly with Closure Phases and Closure Amplitudes
Interferometric imaging now achieves angular resolutions as fine as ~10 ÎĽas, probing scales that are inaccessible to single telescopes. Traditional synthesis imaging methods require calibrated visibilities; however, interferometric calibration is challenging, especially at high frequencies. Nevertheless, most studies present only a single image of their data after a process of "self-calibration," an iterative procedure where the initial image and calibration assumptions can significantly influence the final image. We present a method for efficient interferometric imaging directly using only closure amplitudes and closure phases, which are immune to station-based calibration errors. Closure-only imaging provides results that are as noncommittal as possible and allows for reconstructing an image independently from separate amplitude and phase self-calibration. While closure-only imaging eliminates some image information (e.g., the total image flux density and the image centroid), this information can be recovered through a small number of additional constraints. We demonstrate that closure-only imaging can produce high-fidelity results, even for sparse arrays such as the Event Horizon Telescope, and that the resulting images are independent of the level of systematic amplitude error. We apply closure imaging to VLBA and ALMA data and show that it is capable of matching or exceeding the performance of traditional self-calibration and CLEAN for these data sets
The Zwicky Transient Facility: Data Processing, Products, and Archive
The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey
currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a
47 square degree field with a 600 megapixel camera to scan the entire northern
visible sky at rates of ~3760 square degrees/hour to median depths of g ~ 20.8
and r ~ 20.6 mag (AB, 5sigma in 30 sec). We describe the Science Data System
that is housed at IPAC, Caltech. This comprises the data-processing pipelines,
alert production system, data archive, and user interfaces for accessing and
analyzing the products. The realtime pipeline employs a novel
image-differencing algorithm, optimized for the detection of point source
transient events. These events are vetted for reliability using a
machine-learned classifier and combined with contextual information to generate
data-rich alert packets. The packets become available for distribution
typically within 13 minutes (95th percentile) of observation. Detected events
are also linked to generate candidate moving-object tracks using a novel
algorithm. Objects that move fast enough to streak in the individual exposures
are also extracted and vetted. The reconstructed astrometric accuracy per
science image with respect to Gaia is typically 45 to 85 milliarcsec. This is
the RMS per axis on the sky for sources extracted with photometric S/N >= 10.
The derived photometric precision (repeatability) at bright unsaturated fluxes
varies between 8 and 25 millimag. Photometric calibration accuracy with respect
to Pan-STARRS1 is generally better than 2%. The products support a broad range
of scientific applications: fast and young supernovae, rare flux transients,
variable stars, eclipsing binaries, variability from active galactic nuclei,
counterparts to gravitational wave sources, a more complete census of Type Ia
supernovae, and Solar System objects.Comment: 30 pages, 16 figures, Published in PASP Focus Issue on the Zwicky
Transient Facility (doi: 10.1088/1538-3873/aae8ac
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