1,720,989 research outputs found
A sufficient condition based on the Cauchy-Schwarz inequality for efficient template matching
No full textThe paper proposes a technique aimed at reducing the number of calculations required to carry out an exhaustive template matching process based on the Normalized Cross Correlation (NCC). The technique deploys an effective sufficient condition, relying on the recently introduced concept of bounded partial correlation, that allows rapid elimination of the points that can not provide a better cross-correlation score with respect to the current best candidate. In this paper we devise a novel sufficient condition based on the Cauchy-Schwarz inequality and compare the experimental results with those attained using the standard NCC-based template matching algorithm and the already known sufficient condition based on the Jensen inequality
Fast template matching using bounded partial correlation
No full textThis paper describes a novel, fast template-matching technique, referred to as bounded partial correlation (BPC), based on the normalised cross-correlation (NCC) function. The technique consists in checking at each search position a suitable elimination condition relying on the evaluation of an upper-bound for the NCC function. The check allows for rapidly skipping the positions that cannot provide a better degree of match with respect to the current best-matching one. The upper-bounding function incorporates partial information from the actual cross-correlation function and can be calculated very efficiently using a recursive scheme. We show also a simple improvement to the basic BPC formulation that provides additional computational benefits and renders the technique more robust with respect to the parameters choice
Real-time stereo within the VIDET project
No full textVIDET is a research project active at the University of Bologna and aimed at the development of a mobility aid for the visually impaired. VIDET's approach consists in the conversion of depth data gathered through a stereo-vision system into a 3D model perceivable by the user by means of a wire-actuated haptic interface. In this paper we describe VIDET's PC-based, real-time, stereo-vision system. As for system's description, we outline the structure of the stereo-matching algorithm and address in more detail the optimization strategies that lead us to a fast PC-based implementation. These involve massive reduction of redundant calculations and use of the parallel multimedia instructions available in current general-purpose microprocessors. We provide experimental results showing that the system is capable of recovering correctly the 3D structure of the observed scene and allows for prompt perception of the depth changes generated by moving objects. We also report execution time measurements and compare our stereo system with the PC-based systems from SRI and Point Grey Research. © 2002 Elsevier Science Ltd. All rights reserved
An efficient algorithm for exhaustive template matching based on normalized cross correlation
No full textThis work proposes a novel technique aimed at improving the performance of exhaustive template matching based on the normalized cross correlation (NCC). An effective sufficient condition, capable of rapidly pruning those match candidates that could not provide a better cross correlation score with respect to the current best candidate, can be obtained exploiting an upper bound of the NCC function. This upper bound relies on partial evaluation of the crosscorrelation and can be computed efficiently, yielding a significant reduction of operations compared to the NCC function and allows for reducing the overall number of operations required to carry out exhaustive searches. However, the bounded partial correlation (BPC) algorithm turns out to be significantly data dependent. In this paper we propose a novel algorithm that improves the overall performance of BPC thanks to the deployment of a more selective sufficient condition which allows for rendering the algorithm significantly less data dependent. Experimental results with real images and actual CPU time are reported. © 2003 IEEE
Real-time dense stereo on a personal computer
No full textThis paper presents a stereo algorithm that enables real time dense disparity measurements on standard personal computers. Unlike many other dense stereo algorithms, which are based on two matching phases, the proposed algorithm relies on a single matching phase and allows for rejecting unreliable matches by exploiting violations of the uniqueness constraint and analysing the behaviour of the correlation scores. The overall algorithm has been carefully optimised using very efficient calculation schemes and deploying massively the SIMD parallel processing capabilities available nowadays in state-of-the-art general purpose microprocessors. The paper describes the algorithm and the optimisation strategies, and provides experimental results obtained on stereo pairs with ground-truth as well as execution times measurements
Quantitative evaluation of area-based stereo matching
No full textThis paper presents a quantitative evaluation of two area-based stereo matching approaches aimed at real-time applications. The former approach follows a standard scheme based on a double matching phase (DMP) and aimed at rejecting unreliable disparities by enforcing the left-right consistency constraint. This approach is representative of several implementations known in literature. The latter approach, proposed recently, relies on a single matching phase (SMP) and rejects unreliable matches by detecting violations of the uniqueness constraints. We review first the two approaches and analyse their differences. Successively, we provide quantitative results, using standard stereo pairs with ground truth, aimed at evaluating and comparing the two approaches in terms of matching reliability and speed
Temporal filtering of disparity measurements
No full textThe paper proposes a temporal filtering technique for the disparity measurements generated by area-based stereo-matching algorithms. The technique improves temporal consistency of disparity measurements by reducing the matching errors due to noise affecting the imaging system. Moreover, the technique is capable of increasing the number of correct matches by locating uncertain measurements with a criterion based on statistical assumptions that has proven to be more accurate and selective than those relying on texture operators only which are typically deployed with standard area-based stereo algorithms. © 2001 IEEE
Dense stereo based on the uniqueness constraint
No full textThe paper presents the matching core of a stereo algorithm suitable to real-time applications. Unlike most area-based algorithms, the proposed approach relies on a single matching phase (i.e. do not include the check for left-right consistency). Unreliable disparity measuremnts are primarly detected on the basis of the violation of the uniqueness constraint. In order to further improve the reliability of the matches we enforce additional contraints based on the behaviour of the error function that can be veryfied at a very small computational cost. Experimental results show that the proposed approach provides reliable disparity measurements and that it is significantly fast. © 2002 IEEE
A COMPLETE FOS APPROACH FOR INDOOR CROWDSOURCED MAPPING: CASE STUDY ON SAPIENZA UNIVERSITY OF ROME FACULTIES
No full textA complete fos approach for indoor crowdsourced mapping. Case study on Sapienza University of Rome faculties
Full text linkIndoor mapping is an essential process in several applications such as the visualization of space and its utilization, security and resource planning, emergency planning and location-based alerts and, last but not least, indoor navigation. In this work, a completely free and open-source (FOS) approach to map indoor environments, and to navigate through them, is presented. Our tests were carried out within Sapienza University of Rome public buildings; in detail, Letters and Philosophy faculty and Engineering faculty indoor environments were mapped. To reach this goal, only open source software such as Quantum GIS (QGIS) and open-source platforms like Open Street Map (OSM) and its indoor viewer, Open Level Up (OLU) were adopted. A database of indoor environments of the two faculties, completely compatible with OLU, was created through QGIS. In this way, a public territorial information system of classrooms, offices and laboratories is accessible to everyone who can, hence, add or modify the information, following the principle of crowdsourcing and of Volunteered Geographic Information (VGI). The developed procedure is now standard and its outputs accepted by the OSM community. Hence, the long-term developments of this project are the proposal for the volunteered and cooperative indoor mapping and design of strategic buildings and infrastructures (hospitals, schools, public offices, shopping centers, stations, airports etc.), starting from the available information (indoor layouts) and knowledge acquired through experience of people who normally work inside them and/or visit them frequently. In this context it is possible to state that the development of VGI for internal maps for strategic buildings, infrastructures and denied GNSS environments, not only supports and improves internal and external navigation without interruption, but can also have a significant positive impact on security and emergency management
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