177,403 research outputs found
Numerical equivalence of -divisors and Shioda-Tate formula for arithmetic varieties
No full textLet be an arithmetic variety over the ring of integers of a number field
, with smooth generic fiber . We give a formula that relates the
dimension of the first Arakelov-Chow vector space of with the Mordell-Weil
rank of the Albanese variety of and the rank of the N\'eron-Severi group
of . This is a higher dimensional and arithmetic version of the classical
Shioda-Tate formula for elliptic surfaces. Such analogy is strengthened by the
fact that we show that the numerically trivial arithmetic -divisors
on are exactly the linear combinations of principal ones. This result is
equivalent to the non-degeneracy of the arithmetic intersection pairing in the
argument of divisors, partially confirming [GS94, Conjecture 1].Comment: 18 pages. Minor changes. New Lemma 3.
Mobile Video Surveillance with Low-Bandwidth Low-Latency Video Streaming
No full textThis paper presents a system for remote live video surveillance. Videos are acquired from a fixed camera at 10 fps and QVGA resolution, compressed at 5 or 20 kbit/s with H.264, and streamed to a remote site, where they get processed by an automatic video surveillance system. The target surveillance application performs moving object segmentation and tracking. Both ends (video acquisition and processing) could be connected through a wireless network, specifically GPRS.The whole system is studied and optimized to maintain low latency. The reported experiments demonstrate that the proposed system is able to send up to four video streams over GPRS or E-GPRS network, without significantly affecting the performance of the automatic video surveillance system. Comparative tests have been performed with other existing streaming solutions
Multi-stage Sampling with Boosting Cascades for Pedestrian Detection in Images and Videos
No full textMany works address the problem of object detection by means of machine learning with boosted classifiers. They exploit sliding window search, spanning the whole image: the patches, at all possible positions and sizes, are sent to the classifier. Several methods have been proposed to speed up the search (adding complementary features or using specialized hardware). In this paper we propose a statisticalbased search approach for object detection which uses a Monte Carlo sampling approach for estimating the likelihood density function with Gaussian kernels. The estimation relies on a multi-stage strategy where the proposal distribution is progressively refined by taking into account the feedback of the classifier (i.e. its response). For videos, this approach is plugged in a Bayesian-recursive framework which exploits the temporal coherency of the pedestrians. Several tests on both still images and videos on common datasets are provided in order to demonstrate therelevant speedup and the increased localization accuracy with respect to sliding window strategy using a pedestrian classifier based on covariance descriptors and a cascade of Logitboost classifiers
Mobile Video Surveillance Systems: An Architectural Overview
No full textThe term mobile is now added to most of computer based systems as synonymous of several different concepts, ranging on ubiquitousness, wireless connection, portability, and so on. In a similar manner, also the name mobile video surveillance is spreading, even though it is often misinterpreted with just limited views of it, such as front-end mobile monitoring, wireless video streaming, moving cameras, distributed systems. This chapter presents an overview of mobile video surveillance systems, focusing in particular on architectural aspects (sensors, functional units and sink modules). A short survey of the state of the art is presented. The chapter will also tackle some problems of video streaming and video tracking specifically designed and optimized for mobile video surveillance systems, giving an idea of the best results that can be achieved in these two foundation layers. © 2010 Springer-Verlag
Covariance Descriptors on Moving Regions for Human Detection in Very Complex Outdoor Scenes
No full textThe detection of humans in very complex scenes can be very challenging, due to the performance degradation of classical motion detection and tracking approaches. An alternative approach is the detection of human-like patterns over the whole image. The present paper follows this line by extending Tuzel et al.’s technique [1] based on covariance descriptors and LogitBoost algorithm applied over Riemannian manifolds. Our proposal represents a significant extension of it by: (a) exploiting motion information to focus the attention over areas in which motion is present or was present in the recent past; (b) enriching the human classifier by additional, dedicated cascades trained on positive and negative samples taken from the specific scene; (c) using a rough estimation of the scene perspective, to reduce false detections and improve system performance. This approach is suitable in multi-camera scenarios, since the monolithic block for human-detection remains the same for the whole system, whereas the parameter tuning and set-up of the three proposed extensions (the only camera-dependent parts of the system), are automatically computed for each camera. The approach has been tested on a construction working site in which complexity and dynamics are very high, making human detection a real challenge. The experimental results demonstrate the improvements achieved by the proposed approach
An Open Source Architecture for Low-Latency Video Streaming on PDAs
No full textThis paper presents a open-source system for low-latency video streaming on PDAs, specifically addressing mobile video surveillance requirements. The system is based on H.264 and suitably modified to obtain the best trade-off between image quality and video fluidity, working also at very limited bandwidths. Moreover, the used con- trols allow to keep the number of lost frames very low. A large set of experiments and comparisons have been carried out and the achieved results demonstrate the efficacy and efficiency of our system
Using Monolithic Classifiers On Multi-stage Pedestrian Detection
No full textDespite the many efforts in finding effective feature sets or accurate classifiers for people detection, few works have addressed ways for reducing the computational burden introducedby the sliding window paradigm. This paper proposes a multi-stage procedure for refining the search for pedestrians using the HOG features and the monolithic SVM classifier. The multi-stage procedure is based on particle-based estimation of pdfs and exploits the margin provided by the classifier to draw more particles on the areas where the classifier’s response is higher. This iterative algorithm achieves the same accuracy than sliding window using less particles (and thus being more efficient) and, conversely, is more accurate when configured to work at thesame computational load. Experimental results on publicly available datasets demonstrate that this method, previouslyproposed for boosted classifiers only, can be successfully applied to monolithic classifiers
Contextual Information and Covariance Descriptors for People Surveillance: An Application for Safety of Construction Workers
No full textIn computer science, contextual information can be used both to reduce computations and to increase accuracy. This paper discusses how it can be exploited for people surveillance in very cluttered environments in terms of perspective (i.e., weak scenecalibration) and appearance of the objects of interest (i.e., relevance feedback on the training of a classifier). These techniques are applied to a pedestrian detector that uses a LogitBoost classifier, appropriately modified to work with covariance descriptors which lie on Riemannian manifolds. On each detected pedestrian, a similar classifier is employed to obtain a precise localization of the head. Two novelties on the algorithms are proposed in this case: polar image transformations to better exploit the circular feature of the head appearance and multispectral image derivatives that catch not only luminance but also chrominance variations. The complete approach has been tested on the surveillance of a construction site to detect workers that do not wear the hard hat: in such scenarios, the complexity and dynamics are very high, making pedestrian detection a real challenge
Low-latency Live Video Streaming over Low-Capacity Networks
No full textThis paper presents an effective system for streaming over low-capacity networks (such as GPRS and EGPRS) of live videos with low latency. Existing solutions are either too complex or not suitable to our scope. For this reason, we developed a complete, ready-to-use streaming system based on H.264/AVC codec and UDP/IP stack. The system employs adaptive controls to achieve the best tradeoff between low latency and good video fluency, by keeping the UDP buffer occupancy at the decoder side between two given levels. Our experiments demonstrate that this system is able to transmit live videos at CIF format and 10 fps over GPRS/EGPRS with very low latency (1.73 sec on average, basically due to the network delay), good fluency and average quality, measured with PSNR, of 31 dB on GPRS at 23 kbps at 10 fps
Perspective and Appearance Context for People Surveillance in Open Areas
No full textContextual information can be used both to reduce computationsand to increase accuracy and this paper presentshow it can be exploited for people surveillance in terms ofperspective (i.e. weak scene calibration) and appearance ofthe objects of interest (i.e. relevance feedback on the trainingof a classifier). These techniques are applied to a pedestriandetector that exploits covariance descriptors througha LogitBoost classifier on Riemannian manifolds. The approachhas been tested on a construction working site wherecomplexity and dynamics are very high, making human detectiona real challenge. The experimental results demonstratethe improvements achieved by the proposed approach
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