87,824 research outputs found
Simultaneous Facial Landmark Detection, Pose and Deformation Estimation under Facial Occlusion
Facial landmark detection, head pose estimation, and facial deformation
analysis are typical facial behavior analysis tasks in computer vision. The
existing methods usually perform each task independently and sequentially,
ignoring their interactions. To tackle this problem, we propose a unified
framework for simultaneous facial landmark detection, head pose estimation, and
facial deformation analysis, and the proposed model is robust to facial
occlusion. Following a cascade procedure augmented with model-based head pose
estimation, we iteratively update the facial landmark locations, facial
occlusion, head pose and facial de- formation until convergence. The
experimental results on benchmark databases demonstrate the effectiveness of
the proposed method for simultaneous facial landmark detection, head pose and
facial deformation estimation, even if the images are under facial occlusion.Comment: International Conference on Computer Vision and Pattern Recognition,
201
3D Face Reconstruction by Learning from Synthetic Data
Fast and robust three-dimensional reconstruction of facial geometric
structure from a single image is a challenging task with numerous applications.
Here, we introduce a learning-based approach for reconstructing a
three-dimensional face from a single image. Recent face recovery methods rely
on accurate localization of key characteristic points. In contrast, the
proposed approach is based on a Convolutional-Neural-Network (CNN) which
extracts the face geometry directly from its image. Although such deep
architectures outperform other models in complex computer vision problems,
training them properly requires a large dataset of annotated examples. In the
case of three-dimensional faces, currently, there are no large volume data
sets, while acquiring such big-data is a tedious task. As an alternative, we
propose to generate random, yet nearly photo-realistic, facial images for which
the geometric form is known. The suggested model successfully recovers facial
shapes from real images, even for faces with extreme expressions and under
various lighting conditions.Comment: The first two authors contributed equally to this wor
Image tag completion by local learning
The problem of tag completion is to learn the missing tags of an image. In
this paper, we propose to learn a tag scoring vector for each image by local
linear learning. A local linear function is used in the neighborhood of each
image to predict the tag scoring vectors of its neighboring images. We
construct a unified objective function for the learning of both tag scoring
vectors and local linear function parame- ters. In the objective, we impose the
learned tag scoring vectors to be consistent with the known associations to the
tags of each image, and also minimize the prediction error of each local linear
function, while reducing the complexity of each local function. The objective
function is optimized by an alternate optimization strategy and gradient
descent methods in an iterative algorithm. We compare the proposed algorithm
against different state-of-the-art tag completion methods, and the results show
its advantages
High-contrast imaging at small separation: impact of the optical configuration of two deformable mirrors on dark holes
The direct detection and characterization of exoplanets will be a major
scientific driver over the next decade, involving the development of very large
telescopes and requires high-contrast imaging close to the optical axis. Some
complex techniques have been developed to improve the performance at small
separations (coronagraphy, wavefront shaping, etc). In this paper, we study
some of the fundamental limitations of high contrast at the instrument design
level, for cases that use a combination of a coronagraph and two deformable
mirrors for wavefront shaping. In particular, we focus on small-separation
point-source imaging (around 1 /D). First, we analytically or
semi-analytically analysing the impact of several instrument design parameters:
actuator number, deformable mirror locations and optic aberrations (level and
frequency distribution). Second, we develop in-depth Monte Carlo simulation to
compare the performance of dark hole correction using a generic test-bed model
to test the Fresnel propagation of multiple randomly generated optics static
phase errors. We demonstrate that imaging at small separations requires large
setup and small dark hole size. The performance is sensitive to the optic
aberration amount and spatial frequencies distribution but shows a weak
dependence on actuator number or setup architecture when the dark hole is
sufficiently small (from 1 to 5 /D).Comment: 13 pages, 18 figure
Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium
Understanding excited carrier dynamics in semiconductors is crucial for the
development of photovoltaics and efficient photonic devices. However,
overlapping spectral features in optical/NIR pump-probe spectroscopy often
render assignments of separate electron and hole carrier dynamics ambiguous.
Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin
films are directly and simultaneously observed by attosecond transient
absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium
M_{4,5}-edge (~30 eV). We decompose the ATAS spectra into contributions of
electronic state blocking and photo-induced band shifts at a carrier density of
8*10^{20}cm^{-3}. Separate electron and hole relaxation times are observed as a
function of hot carrier energies. A first order electron and hole decay of ~1
ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous
observation of electrons and holes with ATAS paves the way for investigating
few to sub-femtosecond dynamics of both holes and electrons in complex
semiconductor materials and across junctions.Comment: Includes Supplementary Informatio
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