9,770 research outputs found
The relation between color spaces and compositional data analysis demonstrated with magnetic resonance image processing applications
This paper presents a novel application of compositional data analysis
methods in the context of color image processing. A vector decomposition method
is proposed to reveal compositional components of any vector with positive
components followed by compositional data analysis to demonstrate the relation
between color space concepts such as hue and saturation to their compositional
counterparts. The proposed methods are applied to a magnetic resonance imaging
dataset acquired from a living human brain and a digital color photograph to
perform image fusion. Potential future applications in magnetic resonance
imaging are mentioned and the benefits/disadvantages of the proposed methods
are discussed in terms of color image processing.Comment: 13 pages, 3 figures, short paper, submitted to Austrian Journal of
Statistics compositional data analysis special issue, first revision, fix
rendering error in fig
A WFC3/HST view of the three stellar populations in the Globular Cluster NGC6752
Multi-band Hubble Space Telescope photometry reveals that the main sequence,
sub-giant, and the red giant branch of the globular cluster NGC6752 splits into
three main components in close analogy with the three distinct segments along
its horizontal branch stars. These triple sequences are consistent with three
stellar groups: a stellar population with a chemical composition similar to
field halo stars (population a), a population (c) with enhanced sodium and
nitrogen, depleted carbon and oxygen and enhanced helium abundance (Delta Y
~0.03), and a population (b) with an intermediate (between population a and c)
chemical composition and slightly helium enhanced (Delta Y ~0.01). These
components contain ~25% (population a), ~45% (population b), and ~30%
(population c) of the stars. No radial gradient for the relative numbers of the
three populations has been identified out to about 2.5 half mass radii.Comment: 42 pages, 24 figures, accepted for publication in Ap
On the kinematic separation of field and cluster stars across the Bulge globular NGC 6528
We present deep and precise multi-band photometry of the Galactic Bulge
globular cluster NGC6528. The current dataset includes optical and
near-infrared images collected with ACS/WFC, WFC3/UVIS, and WFC3/IR on board
the Hubble Space Telescope. The images cover a time interval of almost ten
years and we have been able to carry out a proper-motion separation between
cluster and field stars. We performed a detailed comparison in the m_F814W,
m_F606W - m_F814W Color-Magnitude Diagram with two empirical calibrators
observed in the same bands. We found that NGC6528 is coeval with and more
metal-rich than 47Tuc. Moreover, it appears older and more metal-poor than the
super-metal-rich open cluster NGC6791. The current evidence is supported by
several diagnostics (red horizontal branch, red giant branch bump, shape of the
sub-giant branch, slope of the main sequence) that are minimally affected by
uncertainties in reddening and distance. We fit the optical observations with
theoretical isochrones based on a scaled-solar chemical mixture and found an
age of 11 +- 1 Gyr and an iron abundance slightly above solar ([Fe/H = +0.20).
The iron abundance and the old cluster age further support the recent
spectroscopic findings suggesting a rapid chemical enrichment of the Galactic
Bulge.Comment: 14 pages, 12 figures (2 at low resolution); added references;
corrected figure 3, 4, 5, 8 and 9; results unchanged. Erratum to be published
in Ap
On color image quality assessment using natural image statistics
Color distortion can introduce a significant damage in visual quality
perception, however, most of existing reduced-reference quality measures are
designed for grayscale images. In this paper, we consider a basic extension of
well-known image-statistics based quality assessment measures to color images.
In order to evaluate the impact of color information on the measures
efficiency, two color spaces are investigated: RGB and CIELAB. Results of an
extensive evaluation using TID 2013 benchmark demonstrates that significant
improvement can be achieved for a great number of distortion type when the
CIELAB color representation is used
The PAndAS view of the Andromeda satellite system - I. A Bayesian search for dwarf galaxies using spatial and color-magnitude information
We present a generic algorithm to search for dwarf galaxies in photometric
catalogs and apply it to the Pan-Andromeda Archaeological Survey (PAndAS). The
algorithm is developed in a Bayesian framework and, contrary to most
dwarf-galaxy-search codes, makes use of both the spatial and color-magnitude
information of sources in a probabilistic approach. Accounting for the
significant contamination from the Milky Way foreground and from the structured
stellar halo of the Andromeda galaxy, we recover all known dwarf galaxies in
the PAndAS footprint with high significance, even for the least luminous ones.
Some Andromeda globular clusters are also recovered and, in one case,
discovered. We publish a list of the 143 most significant detections yielded by
the algorithm. The combined properties of the 39 most significant isolated
detections show hints that at least some of these trace genuine dwarf galaxies,
too faint to be individually detected. Follow-up observations by the community
are mandatory to establish which are real members of the Andromeda satellite
system. The search technique presented here will be used in an upcoming
contribution to determine the PAndAS completeness limits for dwarf galaxies.
Although here tuned to the search of dwarf galaxies in the PAndAS data, the
algorithm can easily be adapted to the search for any localised overdensity
whose properties can be modeled reliably in the parameter space of any catalog.Comment: 20 pages, 16 figures, 1 table; accepted for publication in ApJ. High
res pdf available at
https://www.dropbox.com/s/7zk7pme2wunwkjv/PAndAS_dwarf_galaxies.pd
The Carnegie-Chicago Hubble Program: Discovery of the Most Distant Ultra-faint Dwarf Galaxy in the Local Universe
Ultra-faint dwarf galaxies (UFDs) are the faintest known galaxies and due to
their incredibly low surface brightness, it is difficult to find them beyond
the Local Group. We report a serendipitous discovery of an UFD, Fornax UFD1, in
the outskirts of NGC 1316, a giant galaxy in the Fornax cluster. The new galaxy
is located at a projected radius of 55 kpc in the south-east of NGC 1316. This
UFD is found as a small group of resolved stars in the Hubble Space Telescope
images of a halo field of NGC 1316, obtained as part of the Carnegie-Chicago
Hubble Program. Resolved stars in this galaxy are consistent with being mostly
metal-poor red giant branch (RGB) stars. Applying the tip of the RGB method to
the mean magnitude of the two brightest RGB stars, we estimate the distance to
this galaxy, 19.0 +- 1.3 Mpc. Fornax UFD1 is probably a member of the Fornax
cluster. The color-magnitude diagram of these stars is matched by a 12 Gyr
isochrone with low metallicity ([Fe/H] ~ -2.4). Total magnitude and effective
radius of Fornax UFD1 are Mv ~ -7.6 +- 0.2 mag and r_eff = 146 +- 9 pc, which
are similar to those of Virgo UFD1 that was discovered recently in the
intracluster field of Virgo by Jang & Lee (2014).Fornax UFD1 is the most
distant known UFD that is confirmed by resolved stars. This indicates that UFDs
are ubiquitous and that more UFDs remain to be discovered in the Fornax
cluster.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letter
- …