7,395 research outputs found
Poisson noise reduction with non-local PCA
Photon-limited imaging arises when the number of photons collected by a
sensor array is small relative to the number of detector elements. Photon
limitations are an important concern for many applications such as spectral
imaging, night vision, nuclear medicine, and astronomy. Typically a Poisson
distribution is used to model these observations, and the inherent
heteroscedasticity of the data combined with standard noise removal methods
yields significant artifacts. This paper introduces a novel denoising algorithm
for photon-limited images which combines elements of dictionary learning and
sparse patch-based representations of images. The method employs both an
adaptation of Principal Component Analysis (PCA) for Poisson noise and recently
developed sparsity-regularized convex optimization algorithms for
photon-limited images. A comprehensive empirical evaluation of the proposed
method helps characterize the performance of this approach relative to other
state-of-the-art denoising methods. The results reveal that, despite its
conceptual simplicity, Poisson PCA-based denoising appears to be highly
competitive in very low light regimes.Comment: erratum: Image man is wrongly name pepper in the journal versio
Sparsity Based Poisson Denoising with Dictionary Learning
The problem of Poisson denoising appears in various imaging applications,
such as low-light photography, medical imaging and microscopy. In cases of high
SNR, several transformations exist so as to convert the Poisson noise into an
additive i.i.d. Gaussian noise, for which many effective algorithms are
available. However, in a low SNR regime, these transformations are
significantly less accurate, and a strategy that relies directly on the true
noise statistics is required. A recent work by Salmon et al. took this route,
proposing a patch-based exponential image representation model based on GMM
(Gaussian mixture model), leading to state-of-the-art results. In this paper,
we propose to harness sparse-representation modeling to the image patches,
adopting the same exponential idea. Our scheme uses a greedy pursuit with
boot-strapping based stopping condition and dictionary learning within the
denoising process. The reconstruction performance of the proposed scheme is
competitive with leading methods in high SNR, and achieving state-of-the-art
results in cases of low SNR.Comment: 13 pages, 9 figure
The X-ray Power Spectral Density Function and Black Hole Mass Estimate for the Seyfert AGN IC 4329a
We present the X-ray broadband power spectral density function (PSD) of the
X-ray-luminous Seyfert IC 4329a, constructed from light curves obtained via
Rossi X-ray Timing Explorer monitoring and an XMM-Newton observation. Modeling
the 3-10 keV PSD using a broken power-law PSD shape, a break in power-law slope
is significantly detected at a temporal frequency of 2.5(+2.5,-1.7) * 10^-6 Hz,
which corresponds to a PSD break time scale T_b of 4.6(+10.1,-2.3) days. Using
the relation between T_b, black hole mass M_BH, and bolometric luminosity as
quantified by McHardy and coworkers, we infer a black hole mass estimate of
M_BH = 1.3(+1.0,-0.3) * 10^8 solar masses and an accretion rate relative to
Eddington of 0.21(+0.06,-0.10) for this source. Our estimate of M_BH is
consistent with other estimates, including that derived by the relation between
M_BH and stellar velocity dispersion. We also present PSDs for the 10-20 and
20-40 keV bands; they lack sufficient temporal frequency coverage to reveal a
significant break, but are consistent with the same PSD shape and break
frequency as in the 3-10 keV band.Comment: Accepted for publication in ApJ. 11 pages, 6 figures (5 color
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