Light, Shadows & Color:
Photometric Image
Formation
Materials on these slides have come from many sources in addition to myself; I am infinitely grateful to these, especially Greg Hager, Silvio Savarese, and
Steve Seitz.
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Module 1 - Image Formation, Slides of Computer Science
Light, Shadows & Color: Photometric Image Formation
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Light, Shadows & Color:
Photometric Image
Formation
Materials on these slides have come from many sources in addition to myself; I am infinitely grateful to these, especially Greg Hager, Silvio Savarese, and
Plan
- (^) Radiometry and the BRDF
- (^) Light and shading models
- (^) The digital camera
Photometric Image Formation
Source: Szeliski book (Fig. 2.14).
Photometric Image Formation
- (^) Three components to pixel brightness - Illumination and light sources - Surfaces and reflection - Camera response
Lights in the real-world
- (^) Real lights are complicated
- (^) Sun-light, incandescent bulbs, fluorescent bulbs
- (^) Different spectra
- (^) Different directions
- (^) Time-varying
- (^) Fluorscence and biochemistry as well. Source: https://
Light Models
- (^) Coarse approximations to real light
- (^) Point light
- (^) Directional
- (^) Spot
- (^) Has a location in space and a distribution over wavelengths
- (^) Area lights
- (^) Light-fields
- (^) Point light
- (^) Environment Map
- (^) Maps incident light directions to color values Source: Image from Pat Hanrahan slides on environment
Surfaces and Reflectance
Source: Szeliski book.
The Bidirectional Reflectance Distribution
Function
- (^) A general model of light scattering Incident light parameters Light parameter Reflected light parameters
- (^) Helmholtz reciprocity
- (^) Simplified form for isotropic materials
BRDF
- (^) Isotropic vs. Anisotropic Isotropi c Anisotropi c Source: Hanrahan
BRDF
- (^) Understanding and modeling the BRDF is critical to realism in graphics as well as various computer vision applications.
- (^) http:// www.disneyanimation .c om/technology/ brdf.html
Diffuse or Lambertian Reflection
- (^) Light is scattered uniformly in all directions.
- (^) The amount of light depends on the angle between the incident light direction and the surface normal. - Lambert’s cosine law