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Efficiently acquiring reflectance fields using patterned illumination / Gaurav Garg (2006)  

Public Titre : Efficiently acquiring reflectance fields using patterned illumination Type de document : Thèse/HDR Auteurs : Gaurav Garg, Auteur Editeur : Californie [USA] : Stanford University Année de publication : 2006 Importance : 100 p. Format : 21 x 30 cm Note générale : bibliographie A dissertation submitted to the department of electrical engineering and the committee on graduate studies of Stanford University in partiall fulfillment of the requirements for the degree of Doctor of Philosophy Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] dispersion [Termes IGN] distribution du coefficient de réflexion bidirectionnelle BRDF [Termes IGN] données 4D [Termes IGN] éclairement lumineux [Termes IGN] flux lumineux [Termes IGN] matrice symétrique [Termes IGN] réflectance [Termes IGN] tenseur Index. décimale : 24.30 Rayonnement électromagnétique Résumé : (auteur) The use of the reflectance fields of real world objects to render realistic looking images is rapidly increasing. The reflectance field describes the transport of light between the light incident on an object and the light exitant from it. This has numerous applications in areas that include entertainment, cultural heritage, digital libraries and space exploration. The central problem with this approach is the lack of fast methods to acquire the reflectance field data. This dissertation addresses this problem and describes a system for acquiring the reflectance field of real world objects that performs many orders of magnitude faster than the previous approaches. The system models the 8D reflectance field as a transport matrix between the 4D incident light field and the 4D exitant light field. It is a challenging task to measure this matrix because of its large size. However, in some cases the matrix is sparse, e.g. in scenes with little or no inter-reflections. To measure such matrices, this thesis describes a hierarchical technique called dual photography which exploits this sparseness to parallelize the acquisition process. This technique, however, performs poorly for scenes with significant diffuse inter-reflections because in such cases the matrix is dense. Fortunately, in these cases the matrix is often data-sparse. Data-sparseness refers to the fact that sub-blocks of the matrix can be well approximated using low-rank representations. Additionally, the transport matrix is symmetric. Symmetry enables simultaneous measurements from both sides, rows and columns, of the transport matrix. These measurements are used to develop a hierarchical acquisition algorithm that can exploit the data-sparseness by a local rank-1 approximation. This technique, called symmetric photography, parallelizes the acquisition for dense but data-sparse transport matrices. In the process, this thesis introduces the use of hierarchical tensors as the underlying data structure to represent data-sparse matrices, specifically through local rank-1 factorizations of the transport matrix. Besides providing an efficient representation for storage, it enables fast acquisition of the approximated transport matrix and fast rendering of the images from the captured matrix. The prototype acquisition system consists of an array of mirrors and a pair of coaxial projector and camera controlled by a computer. The effectiveness of the system is demonstrated with scenes rendered from reflectance fields that were captured by this system. In these renderings one can change the viewpoint as well as relight objects using arbitrary incident light fields. Note de contenu : 1- Introduction 2- Reflectance Field as the Light Transport Matrix 3- Dual Photography 4- Hierarchical Tensors 5- Symmetric Photography 6- Conclusions and Future Work Numéro de notice : 24635 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère Note de thèse : PhD Thesis : Electrical engineering : Stanford University : 2006 DOI : sans En ligne : https://graphics.stanford.edu/papers/ggaurav_thesis/ Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92231

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
24635-01	THESE	Livre	LASTIG	Dépôt en unité	Exclu du prêt

Light Field Photography with a Hand-Held Plenoptic Camera / Ren Ng (2005) 

Public Titre : Light Field Photography with a Hand-Held Plenoptic Camera Type de document : Rapport Auteurs : Ren Ng, Auteur ; Marc Levoy, Auteur ; Mathieu Brédif , Auteur ; Gene Duval, Auteur ; Mark Horowitz, Auteur ; Pat Hanrahan, Auteur Editeur : Californie [USA] : Stanford University Année de publication : 2005 Importance : 11 p. Note générale : bibliographie Computer Science Tech Report, Rapport de recherche 2005-02, number 2005-02 - Apr 2005 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] image numérique Résumé : (auteur) This paper presents a camera that samples the 4D light field on its sensor in a single photographic exposure. This is achieved by inserting a microlens array between the sensor and main lens, creating a plenoptic camera. Each microlens measures not just the total amount of light deposited at that location, but how much light arrives along each ray. By resorting the measured rays of light to where they would have terminated in slightly different, synthetic cameras, we can compute sharp photographs focused at different depths. We show that a linear increase in the resolution of images under each microlens results in a linear increase in the sharpness of the refocused photographs. This property allows us to extend the depth of field of the camera without reducing the aperture, enabling shorter exposures and lower image noise. Especially in the macrophotography regime, we demonstrate that we can also compute synthetic photographs from a range of different viewpoints. These capabilities argue for a different strategy in designing photographic imaging systems. To the photographer, the plenoptic camera operates exactly like an ordinary hand-held camera. We have used our prototype to take hundreds of light field photographs, and we present examples of portraits, high-speed action and macro close-ups. Numéro de notice : 17771 Affiliation des auteurs : MATIS+Ext (1993-2011) Thématique : IMAGERIE/INFORMATIQUE Nature : Rapport de recherche DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=103486

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