author = "Almeida, Igor Rodrigues de and Jung, Claudio Rosito",
          affiliation = "{Federal University of Rio Grande do Sul} and {Federal University 
                         of Rio Grande do Sul}",
                title = "Change detection in human crowds",
            booktitle = "Proceedings...",
                 year = "2013",
               editor = "Boyer, Kim and Hirata, Nina and Nedel, Luciana and Silva, 
         organization = "Conference on Graphics, Patterns and Images, 26. (SIBGRAPI)",
            publisher = "IEEE Computer Society",
              address = "Los Alamitos",
             keywords = "Crowd analysis, Unusual event detection, Video surveillance.",
             abstract = "This paper presents a method to detect unusual behavior in human 
                         crowds based on histograms of velocities in world coordinates. A 
                         combination of background removal and optical flow is used to 
                         extract the global motion at each image frame, discarding small 
                         motion vectors due artifacts such as noise, non-stationary 
                         background pixels and compression issues. Using a calibrated 
                         camera, the global motion can be estimated, and it is used to 
                         build a 2D histogram containing information of speed and direction 
                         for all frames. Each frame is compared with a set of previous 
                         frames by using a histogram comparison metric, resulting in a 
                         similarity vector. This vector is then used to determine changes 
                         in the crowd behavior, also allowing a classification based on the 
                         nature of the change in time: short or long-term changes. The 
                         method was tested on publicly available datasets involving crowded 
  conference-location = "Arequipa, Peru",
      conference-year = "Aug. 5-8, 2013",
             language = "en",
           targetfile = "PID2848451.pdf",
        urlaccessdate = "2021, July 26"