Gradient Vector Flow (GVF) for region of interest detection in interactive videos GABRIEL Q. REZENDE1,3, JOSENIVALDO BENITO1, DIEGO F. DE CARVALHO2, JOÃO DO E. S. B. NETO2, ADILSON GONZAGA 1 USP – University of São Paulo – Departamento de Engenharia Elétrica, Campus São Carlos, Av. Trabalhador SãoCarlense, 400, Z. Code 13566-590, São Carlos, SP, Brazil {grezende, adilson}@sel.eesc.usp.br,
[email protected] 2 USP – University of São Paulo – Instituto de Ciências Matemáticas e de Computação, Campus São Carlos
[email protected],
[email protected] 3 Associated Scientists Ltd. – 1.717 Alfredo Lopes St., Zip Code 13560-460, São Carlos, SP, Brazil
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Abstract. This work presents the use of active contours models by polygonal mask detection, applied in an edition module for a security area interactive training system, thus identifying necessary regions of interest for the communication between scenes of interactive video. 1. Introduction The objective of this system is to offer a modern training system that uses visual simulation and interaction technology to training centers in the security area. So, it’s possible the user immersion in an environment capable of reproducing situations that offer risks, needing immediate reaction of the security guard. For this purpose, it was developed an environment that encloses and reproduces all the scene relevant information, by simulation with a 2D projected film. This information is presented in different media, such as visual and auditory one [1]. In this article, it will be presented the edition module and the active contours method application. 2. Edition Module The Edition Module is an interactive tool implemented for mapping the personages that compose the scene. It can be used as a solution for the connection between video sequence problem, determining the appropriate videos for scene continuity. This mapping is done by means of masks that identify fatal and not fatal regions (figure 1).
Figure 1: Masks demarcated using the tool
3. Active Contours For minimizing the mapping time in mask construction process, interactions with the polygons using active contours method had been carried through, thus automating the process. In this method, the contours are oriented to interest regions by deformations according to energy function minimization. A previous stage of processing video pictures (images) was done, where Sobel and Prewitt operators, and hystogram analysis had been applied. Differently of others proposed techniques for the external energy function for active contours, the GVF [2] technique, in this case, satisfies all the necessary requirements for fulfilling of the edges in the masks. This technique presents better results than other methods due better convergence in concave regions, since the masks are inserted in regions of the personages bodies with joints, presenting in the majority of the cases brusque movements and forming a great number of concavities of difficult mapping. Another advantage of the GVF method is related to the computational time, converging more quickly to interest regions and consequently producing less errors of deformation due to robustness of its external force. References [1] Valerio A. N., Almeida O. C. P., Carvalho F. D. Development of an Image Edition Module of the Interactive System, Sibgrapi 2003, São Carlos, Brazil. [2] Xu C., Prince J. L Gradient Vector Flow: A New External Force for Snakes. IEEE Trans. On image Proc. 1997.
