3,109 research outputs found
Exact Histogram Specification Optimized for Structural Similarity
An exact histogram specification (EHS) method modifies its input image to
have a specified histogram. Applications of EHS include image (contrast)
enhancement (e.g., by histogram equalization) and histogram watermarking.
Performing EHS on an image, however, reduces its visual quality. Starting from
the output of a generic EHS method, we maximize the structural similarity index
(SSIM) between the original image (before EHS) and the result of EHS
iteratively. Essential in this process is the computationally simple and
accurate formula we derive for SSIM gradient. As it is based on gradient
ascent, the proposed EHS always converges. Experimental results confirm that
while obtaining the histogram exactly as specified, the proposed method
invariably outperforms the existing methods in terms of visual quality of the
result. The computational complexity of the proposed method is shown to be of
the same order as that of the existing methods.
Index terms: histogram modification, histogram equalization, optimization for
perceptual visual quality, structural similarity gradient ascent, histogram
watermarking, contrast enhancement
A Rigourous Treatment of the Lattice Renormalization Problem of F_B
The -meson decay constant can be measured on the lattice using a
expansion. To relate the physical quantity to Monte Carlo data one has to know
the renormalization coefficient, , between the lattice operators and their
continuum counterparts. We come back to this computation to resolve
discrepancies found in previous calculations. We define and discuss in detail
the renormalization procedure that allows the (perturbative) computation of
. Comparing the one-loop calculations in the effective Lagrangian approach
with the direct two-loop calculation of the two-point -meson correlator in
the limit of large -quark mass, we prove that the two schemes give
consistent results to order . We show that there is, however, a
renormalization prescription ambiguity that can have sizeable numerical
consequences. This ambiguity can be resolved in the framework of an
improved calculation, and we describe the correct prescription in that case.
Finally we give the numerical values of that correspond to the different
types of lattice approximations discussed in the paper.Comment: 27 pages, 2 figures (Plain TeX, figures in an appended postscript
file
Magnetic and superconducting instabilities of the Hubbard model at the van Hove filling
We use a novel temperature-flow renormalization group technique to analyze
magnetic and superconducting instabilities in the two-dimensional t-t' Hubbard
model for particle densities close to the van Hove filling as a function of the
next-nearest neighbor hopping t'. In the one-loop flow at the van Hove filling,
the characteristic temperature for the flow to strong coupling is suppressed
drastically around t'_c approx. -0.33t, suggesting a quantum critical point
between d-wave pairing at moderate t'>t'_c and ferromagnetism for t'<t'_c. Upon
increasing the particle density in the latter regime the leading instability
occurs in the triplet pairing channel.Comment: 4 pages, to appear in Physical Review Letter
A Phenomenological Study on Lepton Mass Matrix Textures
The three active light neutrinos are used to explain the neutrino
oscillations. The inherently bi-large mixing neutrino mass matrix and the
Fritzsch type, bi-small mixing charged lepton mass matrix are assumed. By
requiring the maximal \nu_\mu-\nu_\tau mixing for the atmospheric neutrino
problem and the mass-squared difference approperiate for the almost maximal
mixing solution to the solar neutrino problem, the following quantities are
predicted: the \nu_e-\nu_\mu mixing, V_{e3}, CP violation in neutrino
oscillations, and the effective electron-neutrino mass relevant to neutrinoless
double beta decays.Comment: 6 pages, revtex, no figures, confusing points corrected,
clarification and refernces adde
Bayes-optimal inverse halftoning and statistical mechanics of the Q-Ising model
On the basis of statistical mechanics of the Q-Ising model, we formulate the
Bayesian inference to the problem of inverse halftoning, which is the inverse
process of representing gray-scales in images by means of black and white dots.
Using Monte Carlo simulations, we investigate statistical properties of the
inverse process, especially, we reveal the condition of the Bayes-optimal
solution for which the mean-square error takes its minimum. The numerical
result is qualitatively confirmed by analysis of the infinite-range model. As
demonstrations of our approach, we apply the method to retrieve a grayscale
image, such as standard image `Lenna', from the halftoned version. We find that
the Bayes-optimal solution gives a fine restored grayscale image which is very
close to the original.Comment: 13pages, 12figures, using elsart.cl
Unveiling the Active Nucleus of Centaurus A
We report new HST WFPC2 and NICMOS observations of the center of the nearest
radio galaxy Centaurus A (NGC 5128) and discuss their implications for our
understanding of the active nucleus and jet. We detect the active nucleus in
the near-IR (K and H) and, for the first time, in the optical (I and V),
deriving the spectral energy distribution of the nucleus from the radio to
X-rays. The optical and part of the near-IR emission can be explained by the
extrapolation of the X-ray power law reddened by A_V~14mag, a value consistent
with other independent estimates.
The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected
in the [FeII] 1.64mic line and presents a morphology similar to that observed
in Pa alpha with a [FeII]/Pa alpha ratio typical of low ionization Seyfert
galaxies and LINERs. NICMOS 3 Pa alpha observations in a 50"x50" circumnuclear
region suggest enhanced star formation (~0.3Msun/yr) at the edges of the
putative bar seen with ISO, perhaps due to shocks driven into the gas.
The light profile, reconstructed from V, H and K observations, shows that
Centaurus A has a core profile with a resolved break at ~4" and suggests a
black--hole mass of ~10^9 Msun. A linear blue structure aligned with the
radio/X-ray jet may indicate a channel of relatively low reddening in which
dust has been swept away by the jet.Comment: 19 pages, 13 figures, Astrophysical Journal, in press. High quality
figures available at http://www.arcetri.astro.it/~marconi/colpic.htm
Mass-Varying Neutrinos from a Variable Cosmological Constant
We consider, in a completely model-independent way, the transfer of energy
between the components of the dark energy sector consisting of the cosmological
constant (CC) and that of relic neutrinos. We show that such a cosmological
setup may promote neutrinos to mass-varying particles, thus resembling a
recently proposed scenario of Fardon, Nelson, and Weiner (FNW), but now without
introducing any acceleronlike scalar fields. Although a formal similarity of
the FNW scenario with the variable CC one can be easily established, one
nevertheless finds different laws for neutrino mass variation in each scenario.
We show that as long as the neutrino number density dilutes canonically, only a
very slow variation of the neutrino mass is possible. For neutrino masses to
vary significantly (as in the FNW scenario), a considerable deviation from the
canonical dilution of the neutrino number density is also needed. We note that
the present `coincidence' between the dark energy density and the neutrino
energy density can be obtained in our scenario even for static neutrino masses.Comment: 8 pages, minor corrections, two references added, to apear in JCA
Infrared Constraints on AGN Tori Models
This work focuses on the properties of dusty tori in active galactic nuclei
(AGN) derived from the comparison of SDSS type 1 quasars with mid-Infrared
(MIR) counterparts and a new, detailed torus model. The infrared data were
taken by the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. Basic
model parameters are constraint, such as the density law of the graphite and
silicate grains, the torus size and its opening angle. A whole variety of
optical depths is supported. The favoured models are those with decreasing
density with distance from the centre, while there is no clear tendency as to
the covering factor, ie small, medium and large covering factors are almost
equally distributed. Based on the models that better describe the observed
SEDs, properties such as the accretion luminosity, the mass of dust, the inner
to outer radius ratio and the hydrogen column density are computed.Comment: 4 pages, 4 figures, to appear in "Infrared Diagnostics of Galaxy
Evolution", ASP Conference Series, Pasadena, 14-16 November 200
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