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A survey of Light Source Detection Methods

A survey of Light Source Detection Methods. Nathan Funk University of Alberta Nov. 2003. What is Light Source Detection?. Problem of Computer Vision Typically given a single image of a scene Where is the light coming from? Goal:

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A survey of Light Source Detection Methods

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  1. A survey ofLight Source Detection Methods Nathan Funk University of Alberta Nov. 2003

  2. What is Light Source Detection? • Problem of Computer Vision • Typically given a single image of a scene • Where is the light coming from? • Goal: • Recoverdirections, intensities, and types(directional, point, area…)of light sources.

  3. Example 1

  4. Example 2

  5. Motivations, Applications • Scene reconstruction • Find shape of objects • Shape from shading • Augmented reality • Place an artificial objectin a real scene • Wrong lighting is obvious to us Real Artificial [Zhang “Illumination Determination…”, 2000]

  6. Common Assumptions • Directional light sources • Lambertian surface • Smooth surfaces • Other: • Analysis of specific object • Known number of sources • Orthographic projection

  7. Pentland (1982) • Statistical approach • Analyse intensity changesin X and Y directions • Only single source • Similar methods: • Lee & Rosenfeld (1985) – targeted for sphere • Brooks & Horn (1985) – attempt to recover shape Y X

  8. Weinshall (1990) • Analyse intensities alongoccluding boundaries • Look for extreme points of intensity profile • Single source • Yang & Yuille (1991) use similar approach • Extended to detect multiple sources [Nillius “Automatic Estimation…”, 2001]

  9. Zhang & Yang (2000) • Uses sphere model • Find cut-off curves High precision estimation of direction • Each cut-off curves identifies the direction of a light source • Detects multiple sources

  10. Wang & Samaras (2002) • Similar to Zhang & Yang • Known geometry • Map arbitrary surface to sphere • Then apply same techniques as Zhang

  11. Li, Lin, Lu, and Shum (2003) • “Multiple-cue Illumination Estimation” • Uses shading, shadows, and specular reflections • First technique to deal with textured objects

  12. Feature Comparison

  13. Challenges • Processing real images is difficult! • Arbitrary unknown objects • Textured objects • Other types of light sources(not just directional ones) • Reflected light

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