13,969 research outputs found
Recognizing point clouds using conditional random fields
Detecting objects in cluttered scenes is a necessary step for many robotic tasks and facilitates the interaction of the robot with its environment. Because of the availability of efficient 3D sensing devices as the Kinect, methods for the recognition of objects in 3D point clouds have gained importance during the last years. In this paper, we propose a new supervised learning approach for the recognition of objects from 3D point clouds using Conditional Random Fields, a type of discriminative, undirected probabilistic graphical model. The various features and contextual relations of the objects are described by the potential functions in the graph. Our method allows for learning and inference from unorganized point clouds of arbitrary sizes and shows significant benefit in terms of computational speed during prediction when compared to a state-of-the-art approach based on constrained optimization.Peer ReviewedPostprint (authorâs final draft
Spatio-temporal Video Parsing for Abnormality Detection
Abnormality detection in video poses particular challenges due to the
infinite size of the class of all irregular objects and behaviors. Thus no (or
by far not enough) abnormal training samples are available and we need to find
abnormalities in test data without actually knowing what they are.
Nevertheless, the prevailing concept of the field is to directly search for
individual abnormal local patches or image regions independent of another. To
address this problem, we propose a method for joint detection of abnormalities
in videos by spatio-temporal video parsing. The goal of video parsing is to
find a set of indispensable normal spatio-temporal object hypotheses that
jointly explain all the foreground of a video, while, at the same time, being
supported by normal training samples. Consequently, we avoid a direct detection
of abnormalities and discover them indirectly as those hypotheses which are
needed for covering the foreground without finding an explanation for
themselves by normal samples. Abnormalities are localized by MAP inference in a
graphical model and we solve it efficiently by formulating it as a convex
optimization problem. We experimentally evaluate our approach on several
challenging benchmark sets, improving over the state-of-the-art on all standard
benchmarks both in terms of abnormality classification and localization.Comment: 15 pages, 12 figures, 3 table
UPGMpp: a Software Library for Contextual Object Recognition
Object recognition is a cornerstone task towards the scene
understanding problem. Recent works in the field boost their perfor-
mance by incorporating contextual information to the traditional use
of the objectsâ geometry and/or appearance. These contextual cues are
usually modeled through Conditional Random Fields (CRFs), a partic-
ular type of undirected Probabilistic Graphical Model (PGM), and are
exploited by means of probabilistic inference methods. In this work we
present the Undirected Probabilistic Graphical Models in C++ library
(UPGMpp), an open source solution for representing, training, and per-
forming inference over undirected PGMs in general, and CRFs in par-
ticular. The UPGMpp library supposes a reliable and comprehensive
workbench for recognition systems exploiting contextual information, in-
cluding a variety of inference methods based on local search, graph cuts,
and message passing approaches. This paper illustrates the virtues of the
library, i.e. it is efficient, comprehensive, versatile, and easy to use, by
presenting a use-case applied to the object recognition problem in home
scenes from the challenging NYU2 dataset.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech. Spanish grant program FPU-MICINN 2010
and the Spanish projects âTAROTH: New developments toward a robot at
homeâ (Ref. DPI2011-25483) and âPROMOVE: Advances in mobile robotics
for promoting independent life of eldersâ (Ref. DPI2014-55826-R
Learning Object Categories From Internet Image Searches
In this paper, we describe a simple approach to learning models of visual object categories from images gathered from Internet image search engines. The images for a given keyword are typically highly variable, with a large fraction being unrelated to the query term, and thus pose a challenging environment from which to learn. By training our models directly from Internet images, we remove the need to laboriously compile training data sets, required by most other recognition approaches-this opens up the possibility of learning object category models âon-the-fly.â We describe two simple approaches, derived from the probabilistic latent semantic analysis (pLSA) technique for text document analysis, that can be used to automatically learn object models from these data. We show two applications of the learned model: first, to rerank the images returned by the search engine, thus improving the quality of the search engine; and second, to recognize objects in other image data sets
- âŠ