Evaluation of distances between color image segmentations

Iberian Conference on Pattern Recognition and Image Analysis (IbPRIA), 2005, Estoril (Portugal)We illustrate the problem of comparing images by means of their color segmentations. A group of seven distances are proposed within the frame of the Integrated Region Matching distance and the employ of Multivariate Gaussian Distributions (MGD) for the color description of image regions. The performance of these distances is examined in tasks such as image retrieval and object recognition using the two segmentation algorithms in [1] and [2]. The best overall results are obtained for both tasks using the graph–partition approach along with the Fréchet distance, outperforming other distances in comparing MGDs.Peer Reviewe

Research at the learning and vision mobile robotics group 2004-2005

Spanish Congress on Informatics (CEDI), 2005, Granada (España)This article presents the current trends on wheeled mobile robotics being pursued at the Learning and Vision Mobile Robotics Group (IRI). It includes an overview of recent results produced in our group in a wide range of areas, including robot localization, color invariance, segmentation, tracking, audio processing and object learning and recognition.This work was supported by projects: 'Supervised learning of industrial scenes by means of an active vision equipped mobile robot.' (J-00063), 'Integration of robust perception, learning, and navigation systems in mobile robotics' (J-0929).Peer Reviewe

Color Constancy and Image Segmentation Techniques for Applications to Mobile Robotics

Aquesta Tesi que pretén proporcionar un conjunt de tècniques per enfrontar-se al problema que suposa la variació del color en les imatges preses des d'una plataforma mòbil per causa del canvi en les condicions d'il·luminació entre diverses vistes d'una certa escena preses en diferents instants i posicions. També tracta el problema de la segmentació de imatges de color per a poder-les utilitzar en tasques associades a les capacitats d'un robot mòbil, com ara la identificació d'objectes o la recuperació d'imatges d'una gran base de dades.Per dur a terme aquests objectius, primerament s'estableix matemàticament la transformació entre colors degut a variacions d'il·luminació. Així es proposa un model continu per la generació del senyal de color com a generalització natural d'altres propostes anteriors. D'aquesta manera es pot estudiar matemàticament i amb generalitat les condicions per l'existència, unicitat i bon comportament de les solucions, i expressar qualsevol tipus d'aplicació entre colors, independentment del tipus de discretització. Així, queda palès la relació íntima entre el problema de la invariància de color i el de la recuperació espectral, que també es planteja a la pràctica. El model desenvolupat es contrasta numèricament amb els de regressió lineal, en termes d'errors de predicció.Un cop establert el model general, s'opta per un model lineal simplificat a l'hora de realitzar els càlculs pràctics i permet alleugerir el nombre dels mateixos. En particular, el mètode proposat es basa en trobar la transformació més probable entre dues imatges a partir del càlcul d'un conjunt de transformacions possibles i de l'estimació de la freqüència i grau d'efectivitat de cadascuna d'elles. Posteriorment, es selecciona el millor candidat d'acord amb la seva versemblança. L'aplicació resultant serveix per transformar els colors de la imatge tal i com es veuria sota les condicions d'il·luminació canòniques.Una vegada el color de les imatges d'una mateixa escena es manté constant, cal procedir a la seva segmentació per extreure'n la informació corresponent a les regions amb color homogeni. En aquesta Tesi es suggereix un algorisme basat en la partició de l'arbre d'expansió mínima d'una imatge mitjançant una mesura local de la probabilitat de les unions entre components. La idea és arribar a una segmentació coherent amb les regions reals, compromís entre particions amb moltes components (sobresegmentades) i amb molt poques (subsegmentades). Un altre objectiu és que l'algorisme sigui prou ràpid com per ser útil en aplicacions de robòtica mòbil. Aquesta característica s'assoleix amb un plantejament local del creixement de regions, tot i que el resultat presenti caràcters globals (color). La possible sobresegmentació es suavitza gràcies al factor probabilístic introduït.L'algorisme de segmentació també hauria de generar segmentacions estables en el temps. Així, l'algorisme referit s'ha ampliat incloent-hi un pas intermedi entre segmentacions que permet de relacionar regions semblants en imatges diferents i propagar cap endavant els reagrupaments de regions fets en anteriors imatges, així si en una imatge unes regions s'agrupen formant-ne una de sola, les regions corresponents en la imatge següent també s'han d'agrupar juntes. D'aquesta manera, dues segmentacions correlatives s'assemblen i es pot mantenir estable la segmentació d'una seqüència.Finalment, es planteja el problema de comparar imatges a partir del seu contingut. Aquesta Tesi es concentra només en la informació de color i, a més de investigar la millor distància entre segmentacions, es busca també mostrar com la invariància de color afecta les segmentacions.Els resultats obtinguts per cada objectiu proposat en aquesta Tesi avalen els punts de vista defensats, i mostren la utilitat dels algorismes, així com el model de color tant per la recuperació espectral com pel càlcul explícit de les transformacions entre colors.This Thesis endeavors providing a set of techniques for facing the problem of color variation in images taken from a mobile platform and caused by the change in the conditions of lighting among several views of a certain scene taken at different instants and positions. It also treats the problem of segmenting color images in order to use them in tasks associated with the capacities of a mobile robot, such as object identification or image retrieval from a large database.In order to carry out these goals, first transformation among colors due to light variations is mathematically established. Thus, a continuous model for the generation of color is proposed as a natural generalization of other former models. In this way, conditions for the existence, uniqueness, and good behavior of the solutions can be mathematically studied with a great generality, and any type of applications among colors can be expressed independently of the discretization scheme applied. Thus, the intimate relation among the problem of color invariance and that of spectral recovery is made evident and studied in practice too. The developed model is numerically contrasted with those of a least squares linear regression in terms of prediction errors.Once the general model is established, a simplified linear version is chosen instead for carrying out the practical calculations while lightening the number of them. In particular, the proposed method is based on finding the likeliest transformation between two images from the calculation of a set of feasible transformations and the estimation of the frequency and the effectiveness degree of each of them. Later, the best candidate is selected in accordance with its likelihood. The resulting application is then able to transform the image colors as they would be seen under the canonical light.After keeping the image colors from a scene constant, it is necessary to proceed to their segmentation to extract information corresponding to regions with homogeneous colors. In this Thesis, an algorithm based on the partition of the minimum spanning tree of an image through a local measure of the likelihood of the unions among components is suggested. The idea is to arrive at a segmentation coherent with the real regions, a trade-off between partitions with many component (oversegmented) and those with fewer components (subsegmented).Another goal is that of obtaining an algorithm fast enough to be useful in applications of mobile robotics. This characteristic is attained by a local approach to region growing, even though the result still shows global feature (color). The possible oversegmentation is softened thanks to a probabilistic factor.The segmentation algorithm should also generate stable segmentations through time. Thus, the aforementioned algorithm has been widened by including an intermediate step that allows to relate similar regions in different images and to propagate forwards the regrouping of regions made in previous images. This way, if in some image some regions are grouped forming only one bigger region, the corresponding regions in the following image will also be grouped together. In this way, two correlatives segmentations resemble each other, keeping the whole segmented sequence stabler.Finally, the problem of comparing images via their content is also studied in this Thesis, focusing on the color information and, besides investigating which is for our aims the best distance between segmentation, also showing how color constancy affects segmentations. The results obtained in each of the goals proposed in this Thesis guarantee the exposed points of view, and show the utility of the algorithms suggested, as well as the color model for the spectral recovery and the explicit calculation of the transformations among colors

A color constancy algorithm for the robust description of images collected from a mobile robot

Trabajo presentado al 9th CIARP celebrado en Puebla (Mexico) del 26 al 29 de octubre de 2004.In mobile robotics, it is necessary to have a robust and efficient way of describing the visual stream provided by a vision system to be used afterwards in tasks such as object recognition. Color histograms are a useful tool to capture and represent color properties of sets of images taken from a certain position. Since those images were obtained at different time and light conditions, their appearance have greatly changed, reducing the performance of the color descriptor. In this work, we develop a color constancy algorithm that copes with the color variation among sets of images taken from nearly the same place. We show that the performance of the color histogram descriptor rises after color constancy, becoming a more robust and useful color descriptor. In the results section, we support that claim with several sets of images of scenes belonging to different positions.This work was supported by the project 'Integration of robust perception, learning, and navigation systems in mobile robotics' (J-0929).Peer Reviewe

A colour constancy algorithm based on the histogram of feasible colour mappings

9 páginas,3 figuras, 1 tablaIberoamerican Congress on Pattern Recognition (CIARP), 2003, Havana (Cuba)Colour is an important cue in many applications in machine vision and image processing. Nevertheless, colour greatly depends upon illumination changes. Colour constancy goal is to keep colour images stable. This paperrsquos contribution to colour constancy lies in estimating both the set and the likelihood of feasible colour mappings. Then, the most likely mapping is selected and the image is rendered as it would be seen under a canonical illuminant. This approach is helpful in tasks where light can be neither controlled nor easily measured since it only makes use of image data, avoiding a common drawback in other colour constancy algorithms. Finally, we check its performance using several sets of images of objects under quite different illuminants and the results are compared to those obtained if the true illuminant colour were known.This work was supported by the project 'Active vision systems based in automatic learning for industrial applications'.Peer Reviewe

A new color constancy algorithm based on the histogram of feasible mappings

International Conference on Image Analysis and Recognition (ICIAR), 2005, Toronto (Canada)Color is an important cue both in machine vision and image processing applications, despite its dependence upon illumination changes. We propose a color constancy algorithm that estimates both the set and the likelihood of feasible color mappings in respect to their frequency and effectiveness. The best among this set is selected to rendered back image colors as seen under a canonical light. Experiments were done to evaluate its performance compared to Finlayson’s 2D gamut–mapping algorithm, outperforming it. Our approach is a helpful alternative wherever illumination is poorly known since it employs only image data.This work was supported by the project 'Integration of robust perception, learning, and navigation systems in mobile robotics' (J-0929).Peer Reviewe

Colour constancy algorithm based on the minimization of the distance between colour histograms

Trabajo presentado al 1st IbPRIA celebrado en Mallorca del 4 al 6 de junio de 2003.Colour is an important clue in many applications in machine vision and image processing. Despite of this, the drwback of color is its dependence upon illumination changes. Coluor constrancy aims to provide colur appearence of objects with stability. This paper presents a simple and robust coluor constrancy algorithm based on a coefficient transformation of the colour coordinates of pixels which goal is to reduce the distance between histograms of two images of similar scenes under different illuminations. Our main contribution is that our algorithm only make use of raw image data contrary to most usual coluor constancy algorithms. We show that our approach is able to cope with the colour change since it substantially reduces the distance between colour histograms.Partially funded by a fellowship of the Government of Catlonia and tge CICYT DPI2001-2223.Peer Reviewe

Tectonic evolution of the Northern Pyrenees. Results of the PYRAMID project

Mary Ford et. al.The aims of the PYRAMID project funded by the Agence Nationale de la Recherche of France, were to investigate and constrain the 3D structural style and architecture of the North Pyrenean retrowedge and foreland basin, their evolution through time, to define the character and role of inherited crustal geometries, to investigate the interactions between deformation, fluids and thermicity in the different structural units, and to carry out source to sink studies In this talk we present a series of restored cross sections through the central and eastern Pyrenean retrowedge to illustrate structural style, amount and type of deformation and how it was accommodated within the upper crust along the orogen. The total amount of convergence appears to have been constant and the timing of onset of convergence was synchronous. However, in the retrowedge the complexity of the Cretaceous oblique rift system has led to high lateral structural variability. Inherited vertical late Variscan faults trending NE-SW to ENE-WSW segment the European crust and have strongly compartmentalised both retrowedge and foreland basin evolution along the orogen. Crustal scale restorations provide new evolutionary models for the geometry and style of inversion of the pre-orogenic hyper-extended rift system where mantle was exhumed in the most distal domain. Numerical models provide insight into retrowedge inversion. A new stratigraphic scheme has been developed for the eastern and central foreland. Subsidence analyses and foreland basin reconstructions document two pulses of convergence (Late Santonian to Early Paleocene and Eocene to Oligocene) separated by a quiet phase during the Paleocene. These phases can be linked to deformation in the North Pyrenean Zone thrust belt. The first phase was caused mainly by inversion and emplacement of the Metamorphic Internal Zone onto external zones associated with subduction of the exhumed mantle domain. Little or no relief was created during this phase although thermochronological data records the beginning of inversion in the eastern retrowedge. Full collision began in Early Eocene, distributed between the pro- and retro wedges, with only about 30% of convergence accommodated in the retrowedge. Low temperature thermochronology data records southward migrating exhumation of the axial zone while external basement massifs were being exhumed in the North Pyrenean Zone. The Cretaceous rift system was inverted by a combined thin-skinned-thick-skinned style with a decoupling level in the Keuper evaporites. The North Pyrenean Frontal thrust consists of a series of inverted Cretaceous rift margin faults, which in the east represent the main breakaway fault system.Peer Reviewe

Colour image segmentation solving hard-constraints on graph partitioning greedy algorithms

International Conference on Pattern Recognition (ICPR), 2000, Barcelona (España)A graph partitioning greedy algorithm is presented. This algorithm avoids the hard-constraints of others similar approaches such as the impossibility for some regions to grow after certain step of the algorithm and the uniqueness of the solution. Nevertheless, it allows attaining global results by local approximations using a generalised concept of not over-segmentation, which includes an energy function, and eliminating the not sub-segmentation criterion using a probabilistic criterion similar to that of annealing. The high-variability region problems such as borders are also eliminated identifying them and distributing their pixels among the other neighbour regions. Thus, it is possible to keep the time complexity of usual graph partitioning greedy algorithm and avoiding its high variability region problems, obtaining better results.This work was supported by the project 'Active vision systems based in automatic learning for industrial applications' ().Peer Reviewe

Visual tracking system for a mobile robot using colour histograms

IFAC Symposium on Intelligent Autonomous Vehicles (IAV), 2004, Lisbon (Portugal)This work describes the visual system of a mobile robot based on a pan-tilt structure which has been endowed with the ability of tracking moving object using merely color information. Moving objects in the field of view of the camera are detected and the color feature of the most relevant regions is selected as the pattern to follow. Color histograms are used as reliable descriptors to model the appearance of objects. In order to handle with illumination changes a simple adaptation scheme is used. Results show that this system is reliable and fast enough to perform real time tracking of a moving object.Peer Reviewe