University of Louisville
Elhabian, Shireen Y.
Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination.
Degree: PhD, 2012, University of Louisville
Various vision tasks are usually confronted by appearance variations due to changes of illumination. For instance, in a recognition system, it has been shown that the variability in human face appearance is owed to changes to lighting conditions rather than person's identity. Theoretically, due to the arbitrariness of the lighting function, the space of all possible images of a fixed-pose object under all possible illumination conditions is infinite dimensional. Nonetheless, it has been proven that the set of images of a convex Lambertian surface under distant illumination lies near a low dimensional linear subspace. This result was also extended to include non-Lambertian objects with non-convex geometry. As such, vision applications, concerned with the recovery of illumination, reflectance or surface geometry from images, would benefit from a low-dimensional generative model which captures appearance variations w.r.t. illumination conditions and surface reflectance properties. This enables the formulation of such inverse problems as parameter estimation. Typically, subspace construction boils to performing a dimensionality reduction scheme, e.g. Principal Component Analysis (PCA), on a large set of (real/synthesized) images of object(s) of interest with fixed pose but different illumination conditions. However, this approach has two major problems. First, the acquired/rendered image ensemble should be statistically significant vis-a-vis capturing the full behavior of the sources of variations that is of interest, in particular illumination and reflectance. Second, the curse of dimensionality hinders numerical methods such as Singular Value Decomposition (SVD) which becomes intractable especially with large number of large-sized realizations in the image ensemble. One way to bypass the need of large image ensemble is to construct appearance subspaces using phenomenological models which capture appearance variations through mathematical abstraction of the reflection process. In particular, the harmonic expansion of the image irradiance equation can be used to derive an analytic subspace to represent images under fixed pose but different illumination conditions where the image irradiance equation has been formulated in a convolution framework. Due to their low-frequency nature, irradiance signals can be represented using low-order basis functions, where Spherical Harmonics (SH) has been extensively adopted. Typically, an ideal solution to the image irradiance (appearance) modeling problem should be able to incorporate complex illumination, cast shadows as well as realistic surface reflectance properties, while moving away from the simplifying assumptions of Lambertian reflectance and single-source distant illumination. By handling arbitrary complex illumination and non-Lambertian reflectance, the appearance model proposed in this dissertation moves the state of the art closer to the ideal solution. This work primarily addresses the geometrical compliance of the hemispherical basis for representing surface…
Advisors/Committee Members: Farag, Aly A., Starr, Thomas L., Starr, Thomas L., Graham, James H., Cohn, Robert W., Abd El Munim, Hossam Eldin H..
Subjects/Keywords: Computer vision; shape reconstruction; computer graphics; frequency space representation; illumination modeling; Electrical and Computer Engineering
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APA (6th Edition):
Elhabian, S. Y. (2012). Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination. (Doctoral Dissertation). University of Louisville. Retrieved from 10.18297/etd/395 ; https://ir.library.louisville.edu/etd/395
Chicago Manual of Style (16th Edition):
Elhabian, Shireen Y. “Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination.” 2012. Doctoral Dissertation, University of Louisville. Accessed May 09, 2021.
10.18297/etd/395 ; https://ir.library.louisville.edu/etd/395.
MLA Handbook (7th Edition):
Elhabian, Shireen Y. “Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination.” 2012. Web. 09 May 2021.
Elhabian SY. Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination. [Internet] [Doctoral dissertation]. University of Louisville; 2012. [cited 2021 May 09].
Available from: 10.18297/etd/395 ; https://ir.library.louisville.edu/etd/395.
Council of Science Editors:
Elhabian SY. Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination. [Doctoral Dissertation]. University of Louisville; 2012. Available from: 10.18297/etd/395 ; https://ir.library.louisville.edu/etd/395