1,878 research outputs found
Photometric Stereo by Hemispherical Metric Embedding
Photometric Stereo methods seek to reconstruct the 3d shape of an object from
motionless images obtained with varying illumination. Most existing methods
solve a restricted problem where the physical reflectance model, such as
Lambertian reflectance, is known in advance. In contrast, we do not restrict
ourselves to a specific reflectance model. Instead, we offer a method that
works on a wide variety of reflectances. Our approach uses a simple yet
uncommonly used property of the problem - the sought after normals are points
on a unit hemisphere. We present a novel embedding method that maps pixels to
normals on the unit hemisphere. Our experiments demonstrate that this approach
outperforms existing manifold learning methods for the task of hemisphere
embedding. We further show successful reconstructions of objects from a wide
variety of reflectances including smooth, rough, diffuse and specular surfaces,
even in the presence of significant attached shadows. Finally, we empirically
prove that under these challenging settings we obtain more accurate shape
reconstructions than existing methods
Single-image RGB Photometric Stereo With Spatially-varying Albedo
We present a single-shot system to recover surface geometry of objects with
spatially-varying albedos, from images captured under a calibrated RGB
photometric stereo setup---with three light directions multiplexed across
different color channels in the observed RGB image. Since the problem is
ill-posed point-wise, we assume that the albedo map can be modeled as
piece-wise constant with a restricted number of distinct albedo values. We show
that under ideal conditions, the shape of a non-degenerate local constant
albedo surface patch can theoretically be recovered exactly. Moreover, we
present a practical and efficient algorithm that uses this model to robustly
recover shape from real images. Our method first reasons about shape locally in
a dense set of patches in the observed image, producing shape distributions for
every patch. These local distributions are then combined to produce a single
consistent surface normal map. We demonstrate the efficacy of the approach
through experiments on both synthetic renderings as well as real captured
images.Comment: 3DV 2016. Project page at http://www.ttic.edu/chakrabarti/rgbps
Photometric stereo for strong specular highlights
Photometric stereo (PS) is a fundamental technique in computer vision known
to produce 3-D shape with high accuracy. The setting of PS is defined by using
several input images of a static scene taken from one and the same camera
position but under varying illumination. The vast majority of studies in this
3-D reconstruction method assume orthographic projection for the camera model.
In addition, they mainly consider the Lambertian reflectance model as the way
that light scatters at surfaces. So, providing reliable PS results from real
world objects still remains a challenging task. We address 3-D reconstruction
by PS using a more realistic set of assumptions combining for the first time
the complete Blinn-Phong reflectance model and perspective projection. To this
end, we will compare two different methods of incorporating the perspective
projection into our model. Experiments are performed on both synthetic and real
world images. Note that our real-world experiments do not benefit from
laboratory conditions. The results show the high potential of our method even
for complex real world applications such as medical endoscopy images which may
include high amounts of specular highlights
A Dictionary-based Approach for Estimating Shape and Spatially-Varying Reflectance
We present a technique for estimating the shape and reflectance of an object
in terms of its surface normals and spatially-varying BRDF. We assume that
multiple images of the object are obtained under fixed view-point and varying
illumination, i.e, the setting of photometric stereo. Assuming that the BRDF at
each pixel lies in the non-negative span of a known BRDF dictionary, we derive
a per-pixel surface normal and BRDF estimation framework that requires neither
iterative optimization techniques nor careful initialization, both of which are
endemic to most state-of-the-art techniques. We showcase the performance of our
technique on a wide range of simulated and real scenes where we outperform
competing methods.Comment: IEEE Intl. Conf. Computational Photography, 201
Photometric Stereo in Participating Media Considering Shape-Dependent Forward Scatter
Images captured in participating media such as murky water, fog, or smoke are
degraded by scattered light. Thus, the use of traditional three-dimensional
(3D) reconstruction techniques in such environments is difficult. In this
paper, we propose a photometric stereo method for participating media. The
proposed method differs from previous studies with respect to modeling
shape-dependent forward scatter. In the proposed model, forward scatter is
described as an analytical form using lookup tables and is represented by
spatially-variant kernels. We also propose an approximation of a large-scale
dense matrix as a sparse matrix, which enables the removal of forward scatter.
Experiments with real and synthesized data demonstrate that the proposed method
improves 3D reconstruction in participating media.Comment: 9 pages, accepted to CVPR 201
A Novel Framework for Highlight Reflectance Transformation Imaging
We propose a novel pipeline and related software tools for processing the multi-light image collections (MLICs) acquired in different application contexts to obtain shape and appearance information of captured surfaces, as well as to derive compact relightable representations of them. Our pipeline extends the popular Highlight Reflectance Transformation Imaging (H-RTI) framework, which is widely used in the Cultural Heritage domain. We support, in particular, perspective camera modeling, per-pixel interpolated light direction estimation, as well as light normalization correcting vignetting and uneven non-directional illumination. Furthermore, we propose two novel easy-to-use software tools to simplify all processing steps. The tools, in addition to support easy processing and encoding of pixel data, implement a variety of visualizations, as well as multiple reflectance-model-fitting options. Experimental tests on synthetic and real-world MLICs demonstrate the usefulness of the novel algorithmic framework and the potential benefits of the proposed tools for end-user applications.Terms: "European Union (EU)" & "Horizon 2020" / Action: H2020-EU.3.6.3. - Reflective societies - cultural heritage and European identity / Acronym: Scan4Reco / Grant number: 665091DSURF project (PRIN 2015) funded by the Italian Ministry of University and ResearchSardinian Regional Authorities under projects VIGEC and Vis&VideoLa
Determination of mass and orbital parameters of a low-mass star HD 213597B
HD 213597 is an eclipsing binary system which was detected by the STEREO
spacecraft and was speculated to host a low-mass stellar companion. We used
high-resolution spectroscopy with the 10-m Hobby-Eberly Telescope and the 1.2-m
telescope in Mt Abu for radial velocity (RV) measurements of this source. We
performed aperture photometry for this star on the STEREO archival data and
thereby confirm the transit signature. We also did follow-up ground-based
photometry with a 10-inch telescope from Mt Abu. The spectroscopic RV
semi-amplitude of the primary (33.39 km s^-1) indicates that the secondary is
an M dwarf making the system a short period F+M eclipsing binary. These RVs
along with the inclination derived from our combined photometric analysis
(i=84.9 degree), enable us to estimate the mass of the secondary as M_B ~ 0.286
M_sun and radius as R_B ~ 0.344 R_sun using an estimated mass M_A ~ 1.3 M_sun
and radius R_B ~ 1.97 R_sun of the primary. Our spectral analysis returned the
following parameters: T_eff = 6625 +/-121 K, [Fe/H] = -0.095 +\-0.08 and log(g)
= 3.72 +/-0.22 for the primary. When log(g) is constrained to a value of 3.96,
we derive T_eff = 6753 +/-52 K and [Fe/H] = -0.025+\-0.05.Comment: 22 pages, 3 figures, Accepted for publication in MNRA
The New Horizons Kuiper Belt Extended Mission
The central objective of the New Horizons prime mission was to make the first
exploration of Pluto and its system of moons. Following that, New Horizons has
been approved for its first extended mission, which has the objectives of
extensively studying the Kuiper Belt environment, observing numerous Kuiper
Belt Objects (KBOs) and Centaurs in unique ways, and making the first close
flyby of the KBO 486958 2014 MU69. This review summarizes the objectives and
plans for this approved mission extension, and briefly looks forward to
potential objectives for subsequent extended missions by New Horizons
STEREO Observations of Hybrid Stars V775 Tau and V483 Tau
In this study, pulsational and physical characteristics of two Scuti
stars, V775 Tau and V483 Tau, are analysed by using four-year high-precision
photometric data of STEREO satellite. Thus, it is aimed to gain new insights
into behaviours of these pulsators and evolution of Scuti,
Dor and Am type stars. The data are taken between 2007--2011 and examined with
the help of the Lomb-Scargle method. The detection precision in the four-year
combined data is around c/d in frequency and mag in
amplitude. It is revealed that V775 Tau exhibits weak pulsation characteristic
which is interpreted as the existence of the interaction between the helium
loss in the partial ionization zone and pulsation intensities. It is also
considered that the absence of strong pulsations is also related to the
evolution status of the star. Further, its periodogram shows low-frequency
peaks. If these oscillations are g-modes, V775 Tau can be thought to be one of
the rare stars that show all Dor, Scuti and Am type
variations. V483 Tau is comparatively more luminous, hotter and has higher
rotational velocity. Therefore, although it shares the same region with V775
Tau in the H-R diagram, it is not considered to be an Am star. Yet, it exactly
overlaps with the Dor stars. These clues as well as g-modes detected
in its periodogram indicate that V483\,Tau is a hybrid star. Finally, both V775
Tau and V483 Tau display period changes whose rates are between and
. Considering the Scuti nature, it may be
speculated that these changes are non-evolutionary.Comment: 14 pages, 7 figures, 8 tables,accepted by the Astrophysics and Space
Science with the manuscript number ASTR-D-18-00290R
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