学位の種別:課程博士University of Tokyo(東京大学

Shi Boxin

施 柏鑫

UTokyo Repository

論 文 の 内 容 の 要 旨 
 
 
 
論文題目    Photometric Stereo for General Reflectance and Lighting 
（実物体反射特性・実環境光源のための照度差ステレオ） 
      氏  名    施 柏鑫  
 
 
 
Understanding the 3D shape information is a fundamental problem in computer vision. 
Among various shape estimation technology, photometric stereo is highlighted for its 
ability to produce detailed surface normal direction at its image resolution. It takes a set 
of images captured under varying illumination and a fixed viewpoint as input. 
Traditional photometric stereo assumes the Lambertian reflectance and distant lighting. 
These assumptions are seldom satisfied in a practical scenario. This dissertation 
generalizes the assumptions for photometric stereo, specifically on reflectance and 
lighting, towards creating a practical surface normal sensor. The proposed approaches 
serve as fundamental support to the design of future cameras which are able to record 
and measure 3D shapes for various applications like culture heritage archive, digital 
museum, virtual reality, 3D scene understanding, and so on.  
 
The first general reflectance solution exploits the reflectance monotonicity for 
estimating elevation angles of surface normal given the azimuth angles to fully 
determine the surface normal. With an assumption that the reflectance includes at least 
one lobe that is a monotonic function of the angle between the surface normal and 
half-vector (bisector of lighting and viewing directions), we prove that elevation angle 
can be uniquely determined when the surface is observed under varying directional 
lights densely and uniformly distributed over the hemisphere. 
 
The second general reflectance solution is built upon a newly developed reflectance 
model. We notice that if the high-frequency reflectance can be neglected, the 
low-frequency component of general reflectance can simply be represented using 
low-order polynomials. Based on this observation, we propose a compact bi-polynomial 
reflectance model to describe the general isotropic reflectance precisely in the 
low-frequency domain. We apply our reflectance model to radiometric image analysis 
problems of estimating reflectance and shape given recorded scene radiance, namely 
reflectometry and photometric stereo, for surfaces with general reflectance. 
 
Both of the proposed solutions for general reflectance have been evaluated by using a 
densely measured reflectance database containing one hundred different materials and 
various types of real-world data. These evaluations cover a diversity of common 
materials in our daily life; hence the experiments prove that our approaches are valid for 
a broad class of reflectance and useful for various practical scenarios. 
 
The third solution is about general lighting. We present a photometric stereo method 
that works with general/unknown lightings and uncontrolled sensors using a coarse 
shape that is given. We show that the coarse shape information, or a shape prior, serves 
to solve two difficult issues: removing shape-light ambiguity in unknown natural 
lightings, and disregarding uncontrolled sensor gains and responses. Our method is 
well-suited to work with a low-cost RGBD camera, whose radiometric characteristics 
are totally unknown. We also show an application to 3D modeling from Internet images, 
where illumination and sensor characteristics are unknown. Effectiveness of the 
proposed method is assessed by quantitative and qualitative evaluations. 
 
The main contributions of this dissertation are three folds: We explore the 
monotonicity of reflectance function and use it for surface normal estimation with 
general reflectance; we inventively propose a new reflectance model in the 
low-frequency domain, which facilitates the reflectometry and photometric stereo 
problems with general reflectance; and we design a practical photometric stereo system 
that works without knowing environment lighting and camera's radiometric response. 
The efforts and achievements in this thesis relax the theoretical assumptions and 
promote the practical capabilities of photometric stereo technique by considering 
general reflectance and lighting.   
 


実物体反射特性・実環境光源のための照度差ステレオ

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実物体反射特性・実環境光源のための照度差ステレオ

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