1,720,962 research outputs found
Accurate 3D reconstruction of dynamic scenes with complex reflectance properties.
Get PDFAccurate 3D geometry modelling is an essential technology for many practical applications (computer generated imagery, assisted surgery, heritage preservation, automated quality control, robotics etc.). While the existing reconstruction methods mainly operate assuming the simplistic Lambertian model, real scenes, static or dynamic, are characterised by arbitrarily complex a priori unknown reflectance properties. The reflectance limitation of the state-of-the-art causes a gap between the practical demand for photometrically arbitrary scene modelling and the constrained applicability scope of existing methods. In response to the gap, this dissertation proposes a solution to the challenging problem of accurate geometric reconstruction of dynamic scenes with arbitrary a priori unknown reflectance. This is achieved by introducing a novel approach which generalises Helmholtz Stereopsis (HS) - a niche technique known to be independent of surface reflectance but till now limited to static scenes requiring sequential acquisition of a large number of input views. The undertaken generalisation extends the technique to dynamic scenes by two mutually tailored developments in response to the shortcomings of conventional HS. These developments are 1) a framework to fundamentally improve the geometric reconstruction accuracy from a small set of input images and 2) the design of a novel wavelength-multiplexing-based pipeline for dynamic scene modelling. Together these constitute a novel practical system which, for the first time, enables reconstruction of dynamic scenes with arbitrary surface properties. To improve the quality of geometric reconstruction by HS, a novel Bayesian formulation of the technique is proposed to replace its sub-optimal maximum likelihood formulation. Further a tailored prior enforcing consistency of per-point depth and normal estimates and related to integrability is developed. The prior purposely exploits the unique ability of HS to characterise the surface by both estimates. The formulation embedded into a coarse-to-fine framework without explicit surface integration achieves unprecedented accuracy and resolution of geometric modelling by HS regardless of reflectance, competitive with what the non-HS state-of-the-art achieves with strictly constrained reflectance. To generalise HS to dynamic scenes, Colour Helmholtz Stereopsis (CL HS) is proposed which utilises wavelength multiplexing for simultaneous acquisition of the minimal set of input images required for reconstruction. The challenges imposed by wavelength multiplexing in CL HS are addressed using a specially designed calibration consisting of two mutually dependent parts: one infers the photometric properties of the acquisition equipment while the other estimates the reconstructed surface chromaticity spatially and propagates it temporally to accommodate dynamic surface deformation. By integrating the proposed coarse-to-fine Bayesian HS with integrability prior into CL HS, remarkable accuracy and resolution of reconstruction are achieved with the minimal input using just three RGB cameras. Evaluation validates the approach by reconstruction of dynamic scenes with arbitrary a priori unknown reflectance, which includes unconstrained spatially varying chromaticity. The reconstructed dynamic sequences exhibit high per-frame geometric accuracy and resolution as well as temporal consistency
Accurate 3D reconstruction of dynamic scenes with complex reflectance properties.
No full textAccurate 3D geometry modelling is an essential technology for many practical applications (computer generated imagery, assisted surgery, heritage preservation, automated quality control, robotics etc.). While the existing reconstruction methods mainly operate assuming the simplistic Lambertian model, real scenes, static or dynamic, are characterised by arbitrarily complex a priori unknown reflectance properties. The reflectance limitation
of the state-of-the-art causes a gap between the practical demand for photometrically arbitrary scene modelling and the constrained applicability scope of existing methods.
In response to the gap, this dissertation proposes a solution to the challenging problem of accurate geometric reconstruction of dynamic scenes with arbitrary a priori unknown reflectance. This is achieved by introducing a novel approach which generalises Helmholtz Stereopsis (HS) - a niche technique known to be independent of surface reflectance but till now limited to static scenes requiring sequential acquisition of a large number of input views. The undertaken generalisation extends the technique to dynamic scenes by two mutually tailored developments in response to the shortcomings of conventional HS. These developments are 1) a framework to fundamentally improve the geometric reconstruction accuracy from a small set of input images and 2) the design of a novel wavelength-multiplexing-based pipeline for dynamic scene modelling. Together these constitute a novel practical system which, for the first time, enables reconstruction of dynamic scenes with arbitrary surface properties.
To improve the quality of geometric reconstruction by HS, a novel Bayesian formulation of the technique is proposed to replace its sub-optimal maximum likelihood formulation.
Further a tailored prior enforcing consistency of per-point depth and normal estimates and related to integrability is developed. The prior purposely exploits the unique ability
of HS to characterise the surface by both estimates. The formulation embedded into a coarse-to-fine framework without explicit surface integration achieves unprecedented accuracy and resolution of geometric modelling by HS regardless of reflectance, competitive with what the non-HS state-of-the-art achieves with strictly constrained reflectance.
To generalise HS to dynamic scenes, Colour Helmholtz Stereopsis (CL HS) is proposed which utilises wavelength multiplexing for simultaneous acquisition of the minimal set of input images required for reconstruction. The challenges imposed by wavelength multiplexing in CL HS are addressed using a specially designed calibration consisting of two mutually dependent parts: one infers the photometric properties of the acquisition equipment while the other estimates the reconstructed surface chromaticity spatially and propagates it temporally to accommodate dynamic surface deformation. By integrating the proposed coarse-to-fine Bayesian HS with integrability prior into CL HS, remarkable accuracy and resolution of reconstruction are achieved with the minimal input using just three RGB cameras. Evaluation validates the approach by reconstruction of dynamic scenes with arbitrary a priori unknown reflectance, which includes unconstrained spatially varying chromaticity. The reconstructed dynamic sequences exhibit high per-frame geometric accuracy and resolution as well as temporal consistency
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Helmholtz Stereopsis Synthetic Dataset
No full textThe dataset consists of synthetic images for three test objects intended to be used as a benchmark for reconstruction via Helmholtz Stereopsis. This also includes ground truth data for quantitative evaluation
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Bayesian Framework for Enhanced Geometric Reconstruction of Complex Objects by Helmholtz Stereopsis
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