Basic Illumination Models

1. Introduction

To create realistic images, computer graphics systems must simulate the behavior of light. Illumination models provide mathematical formulas to calculate the intensity of light on object surfaces.

• Controls realism of scenes
• Based on physical light behavior

2. Light Sources

Light sources emit light that strikes objects in a scene. The position and type of light source affect how objects appear.

• Point light source
• Directional light source
• Ambient light

3. Surface Properties

The appearance of an object depends on how its surface reflects light. Different materials reflect light differently.

• Surface color
• Reflectivity
• Smoothness or roughness

4. Components of Illumination

• Ambient Reflection
• Diffuse Reflection
• Specular Reflection

5. Ambient Reflection

Ambient reflection represents the background light present in a scene that illuminates all objects equally.

• Independent of light direction
• Prevents completely dark areas

6. Diffuse Reflection

Diffuse reflection occurs when light strikes a rough surface and is scattered uniformly in all directions.

• Depends on angle of incidence
• Gives objects their base color

7. Specular Reflection

Specular reflection produces shiny highlights on smooth surfaces where light is reflected in a preferred direction.

• Depends on viewer position
• Creates glossy appearance

8. Phong Illumination Model

The Phong illumination model combines ambient, diffuse, and specular components to calculate surface intensity.

• Most widely used model
• Simple and effective

9. Advantages

• Produces realistic lighting
• Computationally efficient
• Easy to implement

10. Applications

• 3D rendering engines
• Games and animation
• Simulation and visualization

Practice Questions

1. What is an illumination model?
2. List components of illumination.
3. Explain ambient reflection.
4. What is the Phong illumination model?
5. Where are illumination models used?

Practice Task