<p>Any generic computer vision algorithm must be able to copewith the variations in appearance of objects due to differentillumination conditions. While these variations in the shadingof a surface may seem a nuisance, they in fact containinformation about the world. This thesis tries to provide anunderstanding what information can be extracted from theshading in a single image and how to achieve this. One of thechallenges lies in finding accurate models for the wide varietyof conditions that can occur.</p><p>Frequency space representations are powerful tools foranalyzing shading theoretically. Surfaces act as low-passfilters on the illumination making the reflected lightband-limited. Hence, it can be represented by a finite numberof components in the Fourier domain, despite having arbitraryillumination. This thesis derives a basis for shading byrepresenting the illumination in spherical harmonics and theBRDF in a basis for isotropic reflectance. By analyzing thecontributing variance of this basis it is shown how to createfinite dimensional representations for any surface withisotropic reflectance.</p><p>The finite representation is used to analytically derive aprincipal component analysis (PCA) basis of the set of imagesdue to the variations in the illumination and BRDF. The PCA isperformed model-based so that the variations in the images aredescribed by the variations in the illumination and the BRDF.This has a number of advantages. The PCA can be performed overa wide variety of conditions, more than would be practicallypossible if the images were captured or rendered. Also, thereis an explicit mapping between the principal components and theillumination and BRDF so that the PCA basis can be used as aphysical model.</p><p>By combining a database of captured illumination and adatabase of captured BRDFs a general basis for shading iscreated. This basis is used to investigate materialclassification from a single image with known geometry butarbitrary unknown illumination. An image is classified byestimating the coecients in this basis and comparing them to adatabase. Experiments on synthetic data show that materialclassification from reflectance properties is hard. There aremis-classifications and the materials seem to cluster intogroups. The materials are grouped using a greedy algorithm.Experiments on real images show promising results.</p><p><b>Keywords:</b>computer vision, shading, illumination,reflectance, image irradiance, frequency space representations,spherical harmonics, analytic PCA, model-based PCA, materialclassification, illumination estimation</p>

<p>Visual motion carries information about the dynamics of ascene. Automatic interpretation of this information isimportant when designing computer systems forvisualnavigation, surveillance, human-computer interaction, browsingof video databases and other growing applications.</p><p>In this thesis, we address the issue of motionrepresentation for the purpose of detecting and recognizingmotion patterns in video sequences. We localize the motion inspace and time and propose to use local spatio-temporal imagefeatures as primitives when representing and recognizingmotions. To detect such features, we propose to maximize ameasure of local variation of the image function over space andtime and show that such a method detects meaningful events inimage sequences. Due to its local nature, the proposed methodavoids the in.uence of global variations in the scene andovercomes the need for spatial segmentation and tracking priorto motion recognition. These properties are shown to be highlyuseful when recognizing human actions in complexscen es.</p><p>Variations in scale and in relative motions of the cameramay strongly in.uence the structure of image sequences andtherefore the performance of recognition schemes. To addressthis problem, we develop a theory of local spatio-temporaladaptation and show that this approach provides invariance whenanalyzing image sequences under scaling and velocitytransformations. To obtain discriminative representations ofmotion patterns, we also develop several types of motiondescriptors and use them for classifying and matching localfeatures in image sequences. An extensive evaluation of thisapproach is performed and results in the context of the problemof human action recognition are presented. I</p><p>n summary, this thesis provides the following contributions:(i) it introduces the notion of local features in space-timeand demonstrates the successful application of such featuresfor motion interpretation; (ii) it presents a theory and anevaluation of methods for local adaptation with respect toscale and velocity transformations in image sequences and (iii)it presents and evaluates a set of local motion descriptors,which in combination with methods for feature detection andfeature adaptation allow for robust recognition of humanactions in complexs cenes with cluttered and non-stationarybackgrounds as well as camera motion.</p>

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 120-124).

Thesis (M.S.)--University of Florida, 2001. / Title from first page of PDF file. Document formatted into pages; contains vii, 45 p.; also contains graphics. Vita. Includes bibliographical references (p. 43-44).

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Computer Science." Includes bibliographical references (p. 143-154).

Thesis (M.S.)--University of Florida, 2001. / Title from first page of PDF file. Document formatted into pages; contains viii, 49 p.; also contains graphics. Vita. Includes bibliographical references (p. 47-48).

Thesis (Ph. D.)--State University of New York at Buffalo, 2001. / "September, 2001." Includes bibliographical references (leaves 129-137). Also available in print.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 68-69). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 68-69). Also available on the Internet.

Thesis (M. Sc.)--York University, 1999. Graduate Programme in Computer Science. / Typescript. Includes bibliographical references (leaves 90-93). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ39223.