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Author  |
Xavier Perez Sala; Fernando De la Torre; Laura Igual; Sergio Escalera; Cecilio Angulo |
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Title |
Subspace Procrustes Analysis |
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2017 |
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International Journal of Computer Vision |
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IJCV |
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121 |
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3 |
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327–343 |
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Procrustes Analysis (PA) has been a popular technique to align and build 2-D statistical models of shapes. Given a set of 2-D shapes PA is applied to remove rigid transformations. Then, a non-rigid 2-D model is computed by modeling (e.g., PCA) the residual. Although PA has been widely used, it has several limitations for modeling 2-D shapes: occluded landmarks and missing data can result in local minima solutions, and there is no guarantee that the 2-D shapes provide a uniform sampling of the 3-D space of rotations for the object. To address previous issues, this paper proposes Subspace PA (SPA). Given several
instances of a 3-D object, SPA computes the mean and a 2-D subspace that can simultaneously model all rigid and non-rigid deformations of the 3-D object. We propose a discrete (DSPA) and continuous (CSPA) formulation for SPA, assuming that 3-D samples of an object are provided. DSPA extends the traditional PA, and produces unbiased 2-D models by uniformly sampling different views of the 3-D object. CSPA provides a continuous approach to uniformly sample the space of 3-D rotations, being more efficient in space and time. Experiments using SPA to learn 2-D models of bodies from motion capture data illustrate the benefits of our approach. |
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MILAB; HuPBA; no proj |
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Admin @ si @ PTI2017 |
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2841 |
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Xavier Perez Sala; Cecilio Angulo; Sergio Escalera |
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Title |
Biologically Inspired Turn Control in Robot Navigation |
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2011 |
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14th Congrès Català en Intel·ligencia Artificial |
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187-196 |
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An exportable and robust system for turn control using only camera images is proposed for path execution in robot navigation. Robot motion information is extracted in the form of optical flow from SURF robust descriptors of consecutive frames in the image sequence. This information is used to compute the instantaneous rotation angle. Finally, control loop is closed correcting robot displacements when it is requested for a turn command. The proposed system has been successfully tested on the four-legged Sony Aibo robot. |
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Lleida |
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978-1-60750-841-0 |
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CCIA |
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HuPBA;MILAB |
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Admin @ si @ PAE2011a |
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1753 |
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Xavier Otazu; Xim Cerda-Company |
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Title |
The contribution of luminance and chromatic channels to color assimilation |
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2022 |
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Journal of Vision |
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JOV |
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22(6) |
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10 |
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1-15 |
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Color induction is the phenomenon where the physical and the perceived colors of an object differ owing to the color distribution and the spatial configuration of the surrounding objects. Previous works studying this phenomenon on the lsY MacLeod–Boynton color space, show that color assimilation is present only when the magnocellular pathway (i.e., the Y axis) is activated (i.e., when there are luminance differences). Concretely, the authors showed that the effect is mainly induced by the koniocellular pathway (s axis), but not by the parvocellular pathway (l axis), suggesting that when magnocellular pathway is activated it inhibits the koniocellular pathway. In the present work, we study whether parvo-, konio-, and magnocellular pathways may influence on each other through the color induction effect. Our results show that color assimilation does not depend on a chromatic–chromatic interaction, and that chromatic assimilation is driven by the interaction between luminance and chromatic channels (mainly the magno- and the koniocellular pathways). Our results also show that chromatic induction is greatly decreased when all three visual pathways are simultaneously activated, and that chromatic pathways could influence each other through the magnocellular (luminance) pathway. In addition, we observe that chromatic channels can influence the luminance channel, hence inducing a small brightness induction. All these results show that color induction is a highly complex process where interactions between the several visual pathways are yet unknown and should be studied in greater detail. |
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Neurobit; 600.128; 600.120; 600.158 |
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Admin @ si @ OtC2022 |
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3685 |
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Author |
Xavier Otazu; Oriol Pujol |
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Title |
Wavelet based approach to cluster analysis. Application on low dimensional data sets |
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2006 |
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Pattern Recognition Letters |
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PRL |
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27 |
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14 |
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1590–1605 |
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MILAB; CIC; HuPBA |
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BCNPCL @ bcnpcl @ OtP2006 |
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658 |
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Xavier Otazu; Olivier Penacchio; Xim Cerda-Company |
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Title |
Brightness and colour induction through contextual influences in V1 |
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2015 |
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Scottish Vision Group 2015 SGV2015 |
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12 |
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9 |
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1208-2012 |
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Carnoustie; Scotland; March 2015 |
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SGV |
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NEUROBIT;CIC |
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Admin @ si @ OPC2015a |
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2632 |
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Xavier Otazu; Olivier Penacchio; Xim Cerda-Company |
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Title |
An excitatory-inhibitory firing rate model accounts for brightness induction, colour induction and visual discomfort |
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2015 |
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Barcelona Computational, Cognitive and Systems Neuroscience |
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Barcelona; June 2015 |
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BARCCSYN |
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NEUROBIT;CIC |
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Admin @ si @ OPC2015b |
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2634 |
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Author |
Xavier Otazu; Olivier Penacchio; Laura Dempere-Marco |
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An investigation into plausible neural mechanisms related to the the CIWaM computational model for brightness induction |
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2012 |
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2nd Joint AVA / BMVA Meeting on Biological and Machine Vision |
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Brightness induction is the modulation of the perceived intensity of an area by the luminance of surrounding areas. From a purely computational perspective, we built a low-level computational model (CIWaM) of early sensory processing based on multi-resolution wavelets with the aim of replicating brightness and colour (Otazu et al., 2010, Journal of Vision, 10(12):5) induction effects. Furthermore, we successfully used the CIWaM architecture to define a computational saliency model (Murray et al, 2011, CVPR, 433-440; Vanrell et al, submitted to AVA/BMVA'12). From a biological perspective, neurophysiological evidence suggests that perceived brightness information may be explicitly represented in V1. In this work we investigate possible neural mechanisms that offer a plausible explanation for such effects. To this end, we consider the model by Z.Li (Li, 1999, Network:Comput. Neural Syst., 10, 187-212) which is based on biological data and focuses on the part of V1 responsible for contextual influences, namely, layer 2-3 pyramidal cells, interneurons, and horizontal intracortical connections. This model has proven to account for phenomena such as visual saliency, which share with brightness induction the relevant effect of contextual influences (the ones modelled by CIWaM). In the proposed model, the input to the network is derived from a complete multiscale and multiorientation wavelet decomposition taken from the computational model (CIWaM).
This model successfully accounts for well known pyschophysical effects (among them: the White's and modied White's effects, the Todorovic, Chevreul, achromatic ring patterns, and grating induction effects) for static contexts and also for brigthness induction in dynamic contexts defined by modulating the luminance of surrounding areas. From a methodological point of view, we conclude that the results obtained by the computational model (CIWaM) are compatible with the ones obtained by the neurodynamical model proposed here. |
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CIC |
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Admin @ si @ OPD2012a |
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2132 |
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Author |
Xavier Otazu; Olivier Penacchio; Laura Dempere-Marco |
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Title |
Brightness induction by contextual influences in V1: a neurodynamical account |
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2012 |
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Journal of Vision |
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VSS |
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12 |
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9 |
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Brightness induction is the modulation of the perceived intensity of an area by the luminance of surrounding areas and reveals fundamental properties of neural organization in the visual system. Several phenomenological models have been proposed that successfully account for psychophysical data (Pessoa et al. 1995, Blakeslee and McCourt 2004, Barkan et al. 2008, Otazu et al. 2008).
Neurophysiological evidence suggests that brightness information is explicitly represented in V1 and neuronal response modulations have been observed followingluminance changes outside their receptive fields (Rossi and Paradiso, 1999).
In this work we investigate possible neural mechanisms that offer a plausible explanation for such effects. To this end, we consider the model by Z.Li (1999) which is based on biological data and focuses on the part of V1 responsible for contextual influences, namely, layer 2–3 pyramidal cells, interneurons, and horizontal intracortical connections. This model has proven to account for phenomena such as contour detection and preattentive segmentation, which share with brightness induction the relevant effect of contextual influences. In our model, the input to the network is derived from a complete multiscale and multiorientation wavelet decomposition which makes it possible to recover an image reflecting the perceived intensity. The proposed model successfully accounts for well known pyschophysical effects (among them: the White's and modified White's effects, the Todorović, Chevreul, achromatic ring patterns, and grating induction effects). Our work suggests that intra-cortical interactions in the primary visual cortex could partially explain perceptual brightness induction effects and reveals how a common general architecture may account for several different fundamental processes emerging early in the visual pathway. |
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Admin @ si @ OPD2012b |
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2178 |
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Xavier Otazu; Maria Vanrell; C. Alejandro Parraga |
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Title |
Mutiresolution Wavelet Framework Reproduces Induction Effects |
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2007 |
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Perception 36:167–167, supp |
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CAT @ cat @ OVP2007 |
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842 |
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Xavier Otazu; Maria Vanrell; C. Alejandro Parraga |
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Multiresolution Wavelet Framework Models Brightness Induction Effects |
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2008 |
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Vision Research |
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VR |
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48 |
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5 |
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733–751 |
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CAT @ cat @ OVP2008a |
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Xavier Otazu; Maria Vanrell; C. Alejandro Parraga |
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Colour induction effects are modelled by a low-level multiresolution wavelet framework |
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2008 |
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Perception 37(Suppl.): 107 |
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Xavier Otazu; Maria Vanrell |
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Building Perceived Colour Images. |
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2004 |
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CGIV 2004 Second European Conference on Colour in Graphics, Imaging, and Vision, 140:145 |
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Aachen (Germany) |
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Xavier Otazu; Maria Vanrell |
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Perceptual representation of textured images |
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2005 |
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Journal of Imaging Science and Technology, 49(3):262–271 (IF: 0.522) |
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542 |
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Xavier Otazu; Maria Vanrell |
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A surround-induction function to unify assimilation and contrast in a computational model of color apearance |
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2005 |
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Perception supplement, ECVP05 Abstracts, 34: 215 |
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568 |
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Xavier Otazu; Maria Vanrell |
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Several lightness induction effects with a computational multiresolution wavelet framework |
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2006 |
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29th European Conference on Visual Perception (ECVP’06), Perception Suppl s, 32: 56–56 |
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Saint-Petersburg (Russia) |
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CIC |
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no |
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Call Number |
CAT @ cat @ OtV2006 |
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659 |
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