4,058 research outputs found
Colour constancy using von Kries transformations: colour constancy "goes to the Lab"
Colour constancy algorithms aim at correcting colour towards a correct perception within
scenes. To achieve this goal they estimate a white point (the illuminant's colour), and correct
the scene for its in uence. In contrast, colour management performs on input images colour
transformations according to a pre-established input pro le (ICC pro le) for the given con-
stellation of input device (camera) and conditions (illumination situation). The latter case
presents a much more analytic approach (it is not based on an estimation), and is based on
solid colour science and current industry best practises, but it is rather in exible towards cases
with altered conditions or capturing devices. The idea as outlined in this paper is to take up
the idea of working on visually linearised and device independent CIE colour spaces as used
in colour management, and to try to apply them in the eld of colour constancy. For this
purpose two of the most well known colour constancy algorithms White Patch Retinex and
Grey World Assumption have been ported to also work on colours in the CIE LAB colour
space. Barnard's popular benchmarking set of imagery was corrected with the original imple-
mentations as a reference and the modi ed algorithms. The results appeared to be promising,
but they also revealed strengths and weaknesses
Benchmarking and Error Diagnosis in Multi-Instance Pose Estimation
We propose a new method to analyze the impact of errors in algorithms for
multi-instance pose estimation and a principled benchmark that can be used to
compare them. We define and characterize three classes of errors -
localization, scoring, and background - study how they are influenced by
instance attributes and their impact on an algorithm's performance. Our
technique is applied to compare the two leading methods for human pose
estimation on the COCO Dataset, measure the sensitivity of pose estimation with
respect to instance size, type and number of visible keypoints, clutter due to
multiple instances, and the relative score of instances. The performance of
algorithms, and the types of error they make, are highly dependent on all these
variables, but mostly on the number of keypoints and the clutter. The analysis
and software tools we propose offer a novel and insightful approach for
understanding the behavior of pose estimation algorithms and an effective
method for measuring their strengths and weaknesses.Comment: Project page available at
http://www.vision.caltech.edu/~mronchi/projects/PoseErrorDiagnosis/; Code
available at https://github.com/matteorr/coco-analyze; published at ICCV 1
Dynamical Analysis of Nearby ClustErs. Automated astrometry from the ground: precision proper motions over wide field
The kinematic properties of the different classes of objects in a given
association hold important clues about its member's history, and offer a unique
opportunity to test the predictions of the various models of stellar formation
and evolution. DANCe (standing for Dynamical Analysis of Nearby ClustErs) is a
survey program aimed at deriving a comprehensive and homogeneous census of the
stellar and substellar content of a number of nearby (<1kpc) young (<500Myr)
associations. Whenever possible, members will be identified based on their
kinematics properties, ensuring little contamination from background and
foreground sources. Otherwise, the dynamics of previously confirmed members
will be studied using the proper motion measurements. We present here the
method used to derive precise proper motion measurements, using the Pleiades
cluster as a test bench. Combining deep wide field multi-epoch panchromatic
images obtained at various obervatories over up to 14 years, we derive accurate
proper motions for the sources present in the field of the survey. The datasets
cover ~80 square degrees, centered around the Seven Sisters. Using new tools,
we have computed a catalog of 6116907 unique sources, including proper motion
measurements for 3577478 of them. The catalogue covers the magnitude range
between i=12~24mag, achieving a proper motion accuracy <1mas/yr for sources as
faint as i=22.5mag. We estimate that our final accuracy reaches 0.3mas/yr in
the best cases, depending on magnitude, observing history, and the presence of
reference extragalactic sources for the anchoring onto the ICRS.Comment: Accepted for publication in A&
Visual sensor fusion for active security in robotic industrial environments
This work presents a method of information fusion involving data captured by both a standard CCD camera and a ToF camera to be used in the detection of the proximity between a manipulator robot and a human. Both cameras are assumed to be located above the work area of an industrial robot. The fusion of colour images and time of light information makes it possible to know the 3D localization of objects with respect to a world coordinate system. At the same time this allows to know their colour information. Considering that ToF information given by the range camera contains innacuracies including distance error, border error, and pixel saturation, some corrections over the ToF information are proposed and developed to improve the results. The proposed fusion method uses the calibration parameters of both cameras to reproject 3D ToF points, expressed in a common coordinate system for both cameras and a robot arm, in 2D colour images. In addition to this, using the 3D information, the motion detection in a robot industrial environment is achieved, and the fusion of information is applied to the foreground objects previously detected. This
combination of information results in a matrix that links colour and 3D information, giving the possibility of characterising the object by its colour in addition to its 3D localization. Further development of these methods will make it possible to identify objects and their position in the real world, and to use this information to prevent possible collisions between the robot and such objects
Reconstructing Three-decade Global Fine-Grained Nighttime Light Observations by a New Super-Resolution Framework
Satellite-collected nighttime light provides a unique perspective on human
activities, including urbanization, population growth, and epidemics. Yet,
long-term and fine-grained nighttime light observations are lacking, leaving
the analysis and applications of decades of light changes in urban facilities
undeveloped. To fill this gap, we developed an innovative framework and used it
to design a new super-resolution model that reconstructs low-resolution
nighttime light data into high resolution. The validation of one billion data
points shows that the correlation coefficient of our model at the global scale
reaches 0.873, which is significantly higher than that of other existing models
(maximum = 0.713). Our model also outperforms existing models at the national
and urban scales. Furthermore, through an inspection of airports and roads,
only our model's image details can reveal the historical development of these
facilities. We provide the long-term and fine-grained nighttime light
observations to promote research on human activities. The dataset is available
at \url{https://doi.org/10.5281/zenodo.7859205}
Detection of the tulip breaking virus (TBV) in tulips using optical sensors
The tulip breaking virus (TBV) causes severe economic losses for countries that export tulips such as the Netherlands. Infected plants have to be removed from the field as soon as possible. There is an urgent need for a rapid and objective method of screening. In this study, four proximal optical sensing techniques for the detection of TBV in tulip plants were evaluated and compared with a visual assessment by crop experts as well as with an ELISA (enzyme immunoassay) analysis of the same plants. The optical sensor techniques used were an RGB color camera, a spectrophotometer measuring from 350 to 2500 nm, a spectral imaging camera covering a spectral range from 400 to 900 nm and a chlorophyll fluorescence imaging system that measures the photosynthetic activity. Linear discriminant classification was used to compare the results of these optical techniques and the visual assessment with the ELISA score. The spectral imaging system was the best optical technique and its error was only slightly larger than the visual assessment error. The experimental results appear to be promising, and they have led to further research to develop an autonomous robot for the detection and removal of diseased tulip plants in the open field. The application of this robot system will reduce the amount of insecticides and the considerable pressure on labor for selecting diseased plants by the crop expert. © 2010 The Author(s
The X-CLASS - redMaPPer galaxy cluster comparison: I. Identification procedures
We performed a detailed and, for a large part interactive, analysis of the
matching output between the X-CLASS and redMaPPer cluster catalogues. The
overlap between the two catalogues has been accurately determined and possible
cluster positional errors were manually recovered. The final samples comprise
270 and 355 redMaPPer and X-CLASS clusters respectively. X-ray cluster matching
rates were analysed as a function of optical richness. In a second step, the
redMaPPer clusters were correlated with the entire X-ray catalogue, containing
point and uncharacterised sources (down to a few 10^{-15} erg s^{-1} cm^{-2} in
the [0.5-2] keV band). A stacking analysis was performed for the remaining
undetected optical clusters. Main results show that neither of the wavebands
misses any massive cluster (as coded by X-ray luminosity or optical richness).
After correcting for obvious pipeline short-comings (about 10% of the cases
both in optical and X-ray), ~50% of the redMaPPer (down to a richness of 20)
are found to coincide with an X-CLASS cluster; when considering X-ray sources
of any type, this fraction increases to ~ 80%; for the remaining objects, the
stacking analysis finds a weak signal within 0.5 Mpc around the cluster optical
centers. The fraction of clusters totally dominated by AGN-type emission
appears to be of the order of a few percent. Conversely ~ 40% of the X-CLASS
clusters are identified with a redMaPPer (down to a richness of 20) - part of
the non-matches being due to the fact that the X-CLASS sample extends further
out than redMaPPer (z<1 vs z<0.6); extending the correlation down to a richness
of 5, raises the matching rate to ~ 65%.Comment: 15 pages, 20 figures, 2 table
Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
Context: The interaction of the light from astronomical objects with the
constituents of the Earth's atmosphere leads to the formation of telluric
absorption lines in ground-based collected spectra. Correcting for these lines,
mostly affecting the red and infrared region of the spectrum, usually relies on
observations of specific stars obtained close in time and airmass to the
science targets, therefore using precious observing time. Aims: We present
molecfit, a tool for correcting for telluric absorption lines based on
synthetic modelling of the Earth's atmospheric transmission. Molecfit is
versatile and can be used with data obtained with various ground-based
telescopes and instruments. Methods: Molecfit combines a publicly available
radiative transfer code, a molecular line database, atmospheric profiles, and
various kernels to model the instrument line spread function. The atmospheric
profiles are created by merging a standard atmospheric profile representative
of a given observatory's climate, of local meteorological data, and of
dynamically retrieved altitude profiles for temperature, pressure, and
humidity. We discuss the various ingredients of the method, its applicability,
and its limitations. We also show examples of telluric line correction on
spectra obtained with a suite of ESO Very Large Telescope (VLT) instruments.
Results: Compared to previous similar tools, molecfit takes the best results
for temperature, pressure, and humidity in the atmosphere above the observatory
into account. As a result, the standard deviation of the residuals after
correction of unsaturated telluric lines is frequently better than 2% of the
continuum. Conclusion: Molecfit is able to accurately model and correct for
telluric lines over a broad range of wavelengths and spectral resolutions.
(Abridged)Comment: 18 pages, 13 figures, 5 tables, accepted for publication in Astronomy
and Astrophysic
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