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Author |
T. Widemann; Xavier Otazu |
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Title |
Titanias radius and an upper limit on its atmosphere from the September 8, 2001 stellar occultation |
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2009 |
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International Journal of Solar System Studies |
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199 |
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2 |
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458–476 |
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Occultations; Uranus, satellites; Satellites, shapes; Satellites, dynamics; Ices; Satellites, atmospheres |
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On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V=7.2, K0 III star). This was the first-ever observed occultation by this satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professionals, to monitor this unique event, providing fifty-seven occultations chords over three continents, all reported here. Selecting the best 27 occultation chords, and assuming a circular limb, we derive Titania's radius: View the MathML source (1-σ error bar). This implies a density of View the MathML source using the value View the MathML source derived by Taylor [Taylor, D.B., 1998. Astron. Astrophys. 330, 362–374]. We do not detect any significant difference between equatorial and polar radii, in the limit View the MathML source, in agreement with Voyager limb image retrieval during the 1986 flyby. Titania's offset with respect to the DE405 + URA027 (based on GUST86 theory) ephemeris is derived: ΔαTcos(δT)=−108±13 mas and ΔδT=−62±7 mas (ICRF J2000.0 system). Most of this offset is attributable to a Uranus' barycentric offset with respect to DE405, that we estimate to be: View the MathML source and ΔδU=−85±25 mas at the moment of occultation. This offset is confirmed by another Titania stellar occultation observed on August 1st, 2003, which provides an offset of ΔαTcos(δT)=−127±20 mas and ΔδT=−97±13 mas for the satellite. The combined ingress and egress data do not show any significant hint for atmospheric refraction, allowing us to set surface pressure limits at the level of 10–20 nbar. More specifically, we find an upper limit of 13 nbar (1-σ level) at 70 K and 17 nbar at 80 K, for a putative isothermal CO2 atmosphere. We also provide an upper limit of 8 nbar for a possible CH4 atmosphere, and 22 nbar for pure N2, again at the 1-σ level. We finally constrain the stellar size using the time-resolved star disappearance and reappearance at ingress and egress. We find an angular diameter of 0.54±0.03 mas (corresponding to View the MathML source projected at Titania). With a distance of 170±25 parsecs, this corresponds to a radius of 9.8±0.2 solar radii for HIP 106829, typical of a K0 III giant. |
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Joost Van de Weijer; Theo Gevers; A. Gijsenij |
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Edge-Based Color Constancy |
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2007 |
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IEEE Trans. on Image Processing, vol. 16(9):2207–2214 |
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Javier Vazquez; Maria Vanrell; Anna Salvatella; Eduard Vazquez |
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A colour space based on the image content |
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2007 |
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Artificial Intelligence Research and Development, C. Angulo and L. Godo, pp 205–212 IOS Press |
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829 |
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Javier Vazquez; Maria Vanrell; Robert Benavente |
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Title |
Color names as a constraint for Computer Vision problems |
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2010 |
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Proceedings of The CREATE 2010 Conference |
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324–328 |
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Computer Vision Problems are usually ill-posed. Constraining de gamut of possible solutions is then a necessary step. Many constrains for different problems have been developed during years. In this paper, we present a different way of constraining some of these problems: the use of color names. In particular, we will focus on segmentation, representation ans constancy. |
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Gjovik (Norway) |
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CAT @ cat @ VVB2010 |
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1328 |
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Eduard Vazquez; Joost Van de Weijer; Ramon Baldrich |
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Title |
Image Segmentation in the Presence of Shadows and Highligts |
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2008 |
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10th European Conference on Computer Vision |
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5305 |
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1–14 |
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Marseille (France) |
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CAT @ cat @ VVB2008b |
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1013 |
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Javier Vazquez; Maria Vanrell; Ramon Baldrich |
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Towards a Psychophysical Evaluation of Colour Constancy Algorithms |
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2008 |
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4th European Conference on Colour in Graphics, Imaging and Vision Proceedings |
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372–377 |
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Terrassa (Spain) |
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CGIV08 |
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CAT @ cat @ VVB2008a |
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968 |
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Eduard Vazquez; Francesc Tous; Ramon Baldrich; Maria Vanrell |
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Title |
n-Dimensional Distribution Reduction Preserving its Structure |
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2006 |
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Artificial Intelligence Research and Development, M. Polit et al. (Eds.), 146: 167–175 |
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IOS Press |
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CAT @ cat @ VTB2006a |
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681 |
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Javier Vazquez; C. Alejandro Parraga; Maria Vanrell |
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Title |
Ordinal pairwise method for natural images comparison |
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2009 |
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Perception |
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PER |
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38 |
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180 |
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38(Suppl.)ECVP Abstract Supplement
We developed a new psychophysical method to compare different colour appearance models when applied to natural scenes. The method was as follows: two images (processed by different algorithms) were displayed on a CRT monitor and observers were asked to select the most natural of them. The original images were gathered by means of a calibrated trichromatic digital camera and presented one on top of the other on a calibrated screen. The selection was made by pressing on a 6-button IR box, which allowed observers to consider not only the most natural but to rate their selection. The rating system allowed observers to register how much more natural was their chosen image (eg, much more, definitely more, slightly more), which gave us valuable extra information on the selection process. The results were analysed considering both the selection as a binary choice (using Thurstone's law of comparative judgement) and using Bradley-Terry method for ordinal comparison. Our results show a significant difference in the rating scales obtained. Although this method has been used in colour constancy algorithm comparisons, its uses are much wider, eg to compare algorithms of image compression, rendering, recolouring, etc. |
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CAT @ cat @ VPV2009b |
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1191 |
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Javier Vazquez; C. Alejandro Parraga; Maria Vanrell; Ramon Baldrich |
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Title |
Color Constancy Algorithms: Psychophysical Evaluation on a New Dataset |
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2009 |
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Journal of Imaging Science and Technology |
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53 |
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3 |
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031105–9 |
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The estimation of the illuminant of a scene from a digital image has been the goal of a large amount of research in computer vision. Color constancy algorithms have dealt with this problem by defining different heuristics to select a unique solution from within the feasible set. The performance of these algorithms has shown that there is still a long way to go to globally solve this problem as a preliminary step in computer vision. In general, performance evaluation has been done by comparing the angular error between the estimated chromaticity and the chromaticity of a canonical illuminant, which is highly dependent on the image dataset. Recently, some workers have used high-level constraints to estimate illuminants; in this case selection is based on increasing the performance on the subsequent steps of the systems. In this paper we propose a new performance measure, the perceptual angular error. It evaluates the performance of a color constancy algorithm according to the perceptual preferences of humans, or naturalness (instead of the actual optimal solution) and is independent of the visual task. We show the results of a new psychophysical experiment comparing solutions from three different color constancy algorithms. Our results show that in more than a half of the judgments the preferred solution is not the one closest to the optimal solution. Our experiments were performed on a new dataset of images acquired with a calibrated camera with an attached neutral grey sphere, which better copes with the illuminant variations of the scene. |
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CAT @ cat @ VPV2009a |
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1171 |
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Eduard Vazquez; Theo Gevers; M. Lucassen; Joost Van de Weijer; Ramon Baldrich |
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Title |
Saliency of Color Image Derivatives: A Comparison between Computational Models and Human Perception |
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2010 |
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Journal of the Optical Society of America A |
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JOSA A |
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27 |
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3 |
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613–621 |
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In this paper, computational methods are proposed to compute color edge saliency based on the information content of color edges. The computational methods are evaluated on bottom-up saliency in a psychophysical experiment, and on a more complex task of salient object detection in real-world images. The psychophysical experiment demonstrates the relevance of using information theory as a saliency processing model and that the proposed methods are significantly better in predicting color saliency (with a human-method correspondence up to 74.75% and an observer agreement of 86.8%) than state-of-the-art models. Furthermore, results from salient object detection confirm that an early fusion of color and contrast provide accurate performance to compute visual saliency with a hit rate up to 95.2%. |
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CAT @ cat @ VGL2010 |
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1275 |
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Javier Vazquez; G. D. Finlayson; Maria Vanrell |
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A compact singularity function to predict WCS data and unique hues |
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2010 |
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5th European Conference on Colour in Graphics, Imaging and Vision and 12th International Symposium on Multispectral Colour Science |
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33–38 |
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Understanding how colour is used by the human vision system is a widely studied research field. The field, though quite advanced, still faces important unanswered questions. One of them is the explanation of the unique hues and the assignment of color names. This problem addresses the fact of different perceptual status for different colors.
Recently, Philipona and O'Regan have proposed a biological model that allows to extract the reflection properties of any surface independently of the lighting conditions. These invariant properties are the basis to compute a singularity index that predicts the asymmetries presented in unique hues and basic color categories psychophysical data, therefore is giving a further step in their explanation.
In this paper we build on their formulation and propose a new singularity index. This new formulation equally accounts for the location of the 4 peaks of the World colour survey and has two main advantages. First, it is a simple elegant numerical measure (the Philipona measurement is a rather cumbersome formula). Second, we develop a colour-based explanation for the measure. |
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Joensuu, Finland |
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9781617388897 |
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CAT @ cat @ VFV2010 |
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1324 |
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Eduard Vazquez; Ramon Baldrich; Javier Vazquez; Maria Vanrell |
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Topological histogram reduction towards colour segmentation |
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2007 |
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3rd Iberian Conference on Pattern Recognition and Image Analysis (IbPRIA 2007), J. Marti et al. (Eds.) LNCS 4477:55–62 |
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Gerona (Spain) |
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809 |
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Maria Vanrell; Ramon Baldrich; Anna Salvatella; Robert Benavente; Francesc Tous |
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Induction operators for a computational colour-texture representation |
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2004 |
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Computer Vision and Image Understanding, 94(1–3):92–114, ISSN: 1077–3142 (IF: 0.651) |
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453 |
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Eduard Vazquez; Maria Vanrell |
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Eines per al desenvolupament de competencies de enginyeria en un assignatura de Intel·ligencia Artificial |
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2008 |
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V Jornades d’Innovacio Docent (UAB) |
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Area |
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Expedition |
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Conference |
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Notes |
CIC |
Approved |
no |
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| |
Call Number |
CAT @ cat @ VaV2008 |
Serial |
1011 |
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| Permanent link to this record |
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Author |
Maria Vanrell |
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Title |
Exploring the space of behaviour of a texture perception algorithm |
Type |
Report |
| |
Year |
1997 |
Publication |
CVC Technical Report #12 |
Abbreviated Journal |
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Volume |
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Issue |
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Pages |
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Keywords |
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Abstract |
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Address |
CVC (UAB) |
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Corporate Author |
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Thesis |
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Publisher |
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Place of Publication |
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Editor |
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Language |
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Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
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ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
CIC |
Approved |
no |
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Call Number |
CAT @ cat @ Van1997 |
Serial |
523 |
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| Permanent link to this record |
