Jordi Roca. (2012). Constancy and inconstancy in categorical colour perception (Maria Vanrell, & C. Alejandro Parraga, Eds.). Ph.D. thesis, , .
Abstract: To recognise objects is perhaps the most important task an autonomous system, either biological or artificial needs to perform. In the context of human vision, this is partly achieved by recognizing the colour of surfaces despite changes in the wavelength distribution of the illumination, a property called colour constancy. Correct surface colour recognition may be adequately accomplished by colour category matching without the need to match colours precisely, therefore categorical colour constancy is likely to play an important role for object identification to be successful. The main aim of this work is to study the relationship between colour constancy and categorical colour perception. Previous studies of colour constancy have shown the influence of factors such the spatio-chromatic properties of the background, individual observer's performance, semantics, etc. However there is very little systematic study of these influences. To this end, we developed a new approach to colour constancy which includes both individual observers' categorical perception, the categorical structure of the background, and their interrelations resulting in a more comprehensive characterization of the phenomenon. In our study, we first developed a new method to analyse the categorical structure of 3D colour space, which allowed us to characterize individual categorical colour perception as well as quantify inter-individual variations in terms of shape and centroid location of 3D categorical regions. Second, we developed a new colour constancy paradigm, termed chromatic setting, which allows measuring the precise location of nine categorically-relevant points in colour space under immersive illumination. Additionally, we derived from these measurements a new colour constancy index which takes into account the magnitude and orientation of the chromatic shift, memory effects and the interrelations among colours and a model of colour naming tuned to each observer/adaptation state. Our results lead to the following conclusions: (1) There exists large inter-individual variations in the categorical structure of colour space, and thus colour naming ability varies significantly but this is not well predicted by low-level chromatic discrimination ability; (2) Analysis of the average colour naming space suggested the need for an additional three basic colour terms (turquoise, lilac and lime) for optimal colour communication; (3) Chromatic setting improved the precision of more complex linear colour constancy models and suggested that mechanisms other than cone gain might be best suited to explain colour constancy; (4) The categorical structure of colour space is broadly stable under illuminant changes for categorically balanced backgrounds; (5) Categorical inconstancy exists for categorically unbalanced backgrounds thus indicating that categorical information perceived in the initial stages of adaptation may constrain further categorical perception.
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Jordi Gonzalez, X. Varona, Xavier Roca, & Juan J. Villanueva. (2001). Human Activity Learning and Recognition from Appearance..
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Jordi Gonzalez, X. Varona, Xavier Roca, & Juan J. Villanueva. (2003). Automatic Keyframing of Human Actions for Computer Animation.
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Jordi Gonzalez, X. Varona, Xavier Roca, & Juan J. Villanueva. (2003). A Human Action Comparison Framework for Motion Understanding.
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Jordi Gonzalez, X. Varona, Juan J. Villanueva, & Xavier Roca. (2001). On-line Human Activity Recognition for Video Surveillance..
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Jordi Gonzalez, Thomas B. Moeslund, & Liang Wang. (2012). Semantic Understanding of Human Behaviors in Image Sequences: From video-surveillance to video-hermeneutics. CVIU - Computer Vision and Image Understanding, 116(3), 305–306.
Abstract: Purpose: Atheromatic plaque progression is affected, among others phenomena, by biomechanical, biochemical, and physiological factors. In this paper, the authors introduce a novel framework able to provide both morphological (vessel radius, plaque thickness, and type) and biomechanical (wall shear stress and Von Mises stress) indices of coronary arteries.Methods: First, the approach reconstructs the three-dimensional morphology of the vessel from intravascular ultrasound (IVUS) and Angiographic sequences, requiring minimal user interaction. Then, a computational pipeline allows to automatically assess fluid-dynamic and mechanical indices. Ten coronary arteries are analyzed illustrating the capabilities of the tool and confirming previous technical and clinical observations.Results: The relations between the arterial indices obtained by IVUS measurement and simulations have been quantitatively analyzed along the whole surface of the artery, extending the analysis of the coronary arteries shown in previous state of the art studies. Additionally, for the first time in the literature, the framework allows the computation of the membrane stresses using a simplified mechanical model of the arterial wall.Conclusions: Circumferentially (within a given frame), statistical analysis shows an inverse relation between the wall shear stress and the plaque thickness. At the global level (comparing a frame within the entire vessel), it is observed that heavy plaque accumulations are in general calcified and are located in the areas of the vessel having high wall shear stress. Finally, in their experiments the inverse proportionality between fluid and structural stresses is observed.
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Jordi Gonzalez, & Thomas B. Moeslund. (2008). Tracking Humans for the Evaluation of their Motion in Image Sequences.
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Jordi Gonzalez, Josep M. Gonfaus, Carles Fernandez, & Xavier Roca. (2011). Exploiting Natural-Language Interaction in Video Surveillance Systems. In V&L Net Workshop on Vision and Language.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2003). Automatic Keyframing of Human Actions for Computer Animation.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2003). A Human Action Comparison Framework for Motion Understanding.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2003). Human Sequence Evaluation: towards Knowledge-based Scene Interpretations.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2004). Analysis of Human Walking Based on aSpaces.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2004). Situation Graph Trees for Human Behavior Modeling.
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Jordi Gonzalez, J. Varona, Xavier Roca, & Juan J. Villanueva. (2005). A Comparison Framework for Walking Performances using aSpaces. Electronic Letters on Computer Vision and Image Analysis, Special Issue on articulated Motion, 5(3):105–116 (Electronic Letters: IF: 1.016).
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Jordi Gonzalez, Dani Rowe, Juan Andrade, & Juan J. Villanueva. (2006). Efficient Management of Multiple Agent Tracking Through Observation Handling.
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