73,364 research outputs found
Interactive Extraction of High-Frequency Aesthetically-Coherent Colormaps
Color transfer functions (i.e. colormaps) exhibiting a high frequency luminosity component have proven to be useful in the visualization of data where feature detection or iso-contours recognition is essential. Having these colormaps also display a wide range of color and an aesthetically pleasing composition holds the potential to further aid image understanding and analysis. However producing such colormaps in an efficient manner with current colormap creation tools is difficult. We hereby demonstrate an interactive technique for extracting colormaps from artwork and pictures. We show how the rich and careful color design and dynamic luminance range of an existing image can be gracefully captured in a colormap and be utilized effectively in the exploration of complex datasets
On the Detectability of Lyman-alpha Emission in Star-forming Galaxies: The Role of Dust
Lyman-alpha is now widely used to investigate the galaxy formation and
evolution in the high redshift universe. However, without a rigorous
understanding of the processes which regulate the Lya escape fraction, physical
interpretations of high-z observations remain questionable. We examine six
nearby star-forming galaxies to disentangle the role of the dust from other
parameters such as gas kinematics, geometry and ISM morphology in the
obscuration of Ly-alpha. Thereby we aim to understand the Ly-a escape physics
and infer the implications for high-redshift studies. We use HST/ACS to produce
continuum-subtracted Lya maps, and ground-based observations (ESO/NTT and NOT)
to map the Halpha emission and the extinction E(B-V) in the gas phase derived
from the Balmer decrement Halpha/Hbeta. When large outflows are present, the
Lya emission appears not to correlate with the dust content, confirming the
role of the HI kinematics in the escape of Lya photons. In the case of a dense,
static HI covering, we observe a damped absorption with a declining
relationship between Lya and E(B-V). We found that the Lya escape fraction does
not exceed 10% in all our galaxies and is mostly about 3% or below. Finally,
because of the radiative transfer complexity of the Lya line, star formation
rate based on Lya luminosity is underestimated with respect to that derived
from UV luminosity. The failure of simple dust correction to recover the
intrinsic Lya/Ha ratio or the total star formation rate should prompt us to be
more cautious when interpreting high-z observations and related properties,
such as SFRs based on Lya alone. To this end we propose a more realistic
calibration for SFR(Lya) which accounts for dust attenuation and resonant
scattering effects via the Lya escape fraction.Comment: Accepted for publication in A&A, 19 pages, 15 figure
Infrared Photometry and Dust Absorption in Highly Inclined Spiral Galaxies
We present JHK surface photometry of 15 highly inclined, late-type (Sab-Sc)
spirals and investigate the quantitative effects of dust extinction. Using the
(J - H, H - K) two-color diagram, we compare the color changes along the minor
axis of each galaxy to the predictions from different models of radiative
transfer. Models in which scattering effects are significant and those with
more than a small fraction of the light sources located near the edge of the
dust distribution do not produce enough extinction to explain the observed
color gradients across disk absorption features. The optical depth in dust near
the plane as deduced from the color excess depends sensitively on the adopted
dust geometry, ranging from tau = 4 to 15 in the visual band. This suggests
that a realistic model of the dust distribution is required, even for infrared
photometry, to correct for dust extinction in the bulges of nearly edge-on
systems.Comment: Accepted for publication in the March 1996 AJ. LaTex source which
generates 27 pages of text and tables (no figures). Complete (text + figs)
compressed Postscript preprint is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/inclined.ps.Z (854 Mbyte
Testing the Recovery of Intrinsic Galaxy Sizes and Masses of z~2 Massive Galaxies Using Cosmological Simulations
Accurate measurements of galaxy masses and sizes are key to tracing galaxy
evolution over time. Cosmological zoom-in simulations provide an ideal test bed
for assessing the recovery of galaxy properties from observations. Here, we
utilize galaxies with at z~1.7-2 from the
MassiveFIRE cosmological simulation suite, part of the Feedback in Realistic
Environments (FIRE) project. Using mock multi-band images, we compare intrinsic
galaxy masses and sizes to observational estimates. We find that observations
accurately recover stellar masses, with a slight average underestimate of ~0.06
dex and a ~0.15 dex scatter. Recovered half-light radii agree well with
intrinsic half-mass radii when averaged over all viewing angles, with a
systematic offset of ~0.1 dex (with the half-light radii being larger) and a
scatter of ~0.2 dex. When using color gradients to account for mass-to-light
variations, recovered half-mass radii also exceed the intrinsic half-mass radii
by ~0.1 dex. However, if not properly accounted for, aperture effects can bias
size estimates by ~0.1 dex. No differences are found between the mass and size
offsets for star-forming and quiescent galaxies. Variations in viewing angle
are responsible for ~25% of the scatter in the recovered masses and sizes. Our
results thus suggest that the intrinsic scatter in the mass-size relation may
have previously been overestimated by ~25%. Moreover, orientation-driven
scatter causes the number density of very massive galaxies to be overestimated
by ~0.5 dex at .Comment: Published in the Astrophysical Journal Letters (7 pages, 5 figures;
updated to match published version
Photorealistic Style Transfer with Screened Poisson Equation
Recent work has shown impressive success in transferring painterly style to
images. These approaches, however, fall short of photorealistic style transfer.
Even when both the input and reference images are photographs, the output still
exhibits distortions reminiscent of a painting. In this paper we propose an
approach that takes as input a stylized image and makes it more photorealistic.
It relies on the Screened Poisson Equation, maintaining the fidelity of the
stylized image while constraining the gradients to those of the original input
image. Our method is fast, simple, fully automatic and shows positive progress
in making a stylized image photorealistic. Our results exhibit finer details
and are less prone to artifacts than the state-of-the-art.Comment: presented in BMVC 201
Analysis of Dynamic Brain Imaging Data
Modern imaging techniques for probing brain function, including functional
Magnetic Resonance Imaging, intrinsic and extrinsic contrast optical imaging,
and magnetoencephalography, generate large data sets with complex content. In
this paper we develop appropriate techniques of analysis and visualization of
such imaging data, in order to separate the signal from the noise, as well as
to characterize the signal. The techniques developed fall into the general
category of multivariate time series analysis, and in particular we extensively
use the multitaper framework of spectral analysis. We develop specific
protocols for the analysis of fMRI, optical imaging and MEG data, and
illustrate the techniques by applications to real data sets generated by these
imaging modalities. In general, the analysis protocols involve two distinct
stages: `noise' characterization and suppression, and `signal' characterization
and visualization. An important general conclusion of our study is the utility
of a frequency-based representation, with short, moving analysis windows to
account for non-stationarity in the data. Of particular note are (a) the
development of a decomposition technique (`space-frequency singular value
decomposition') that is shown to be a useful means of characterizing the image
data, and (b) the development of an algorithm, based on multitaper methods, for
the removal of approximately periodic physiological artifacts arising from
cardiac and respiratory sources.Comment: 40 pages; 26 figures with subparts including 3 figures as .gif files.
Originally submitted to the neuro-sys archive which was never publicly
announced (was 9804003
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