This paper presents a novel approach to incorporate spatial information in the bag-ofvisual-words model for category level and scene classification. In the traditional bag-ofvisual-words model, feature vectors are histograms of visual words. This representation is appearance based and does not contain any information regarding the arrangement of the visual words in the 2D image space. In this framework, we present a simple and efficient way to infuse spatial information. Particularly, we are interested in explicit global relationships among the spatial positions of visual words. Therefore, we take advantage of the orientation of the segments formed by Pairs of Identical visual Words (PIW). An evenly distributed normalized histogram of angles of PIW is computed. Histograms produced by each word type constitute a powerful description of intra type visual words relationships. Experiments on challenging datasets demonstrate that our method is competitive with the concurrent ones. We also show that, our method provides important complementary information to the spatial pyramid matching and can improve the overall performance.
Bedload sediment transport of two-size coarse spherical particle mixtures in a turbulent supercritical flow was analyzed with image and particle tracking velocimetry algorithms in a two-dimensional flume. The image processing procedure is entirely presented. Experimental results, including the size, the position, the trajectory, the state of movement (rest, rolling, and saltation), and the neighborhood configuration of each bead, were compared with a previous one-size experiment. Analysis of the solid discharge along the vertical displayed only one peak of rolling in the two-size bed, whereas three peaks of rolling appeared in the one-size case due to a larger collective motion. The same contrast is evidenced in spatio-temporal diagrams where the two-size mixtures are characterized by the predominance of saltation and a smaller number of transitions between rest and rolling. The segregation of fine particles in a bed formed by larger particles was analyzed taking into account the neighborhood configurations.
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