1 CSCE 441: Computer Graphics Lighting Jinxiang Chai

Scan conversion 3D Rendering pipeline Modeling transformation lighting Viewing transformation Project transformation Clipping Image Transform into 3D world system Illuminate according to lighting and reflectance Transform into 3D camera coordinate system Transform into 2D camera system Clip primitives outside camera’s view Draw pixels (includes texturing, hidden surface, etc.)

Scan conversion 3D Rendering pipeline Modeling transformation lighting Viewing transformation Project transformation Clipping Image Transform into 3D world system Illuminate according to lighting and reflectance Transform into 3D camera coordinate system Transform into 2D camera system Clip primitives outside camera’s view Draw pixels (includes texturing, hidden surface, etc.)

Outline Ambient, diffuse and specular light Light attenuation & spot lights Readings: HB 17-1,12- 2,17-3

Lighting/Illumination Color is a function of how light reflects from surfaces to the eye Global illumination accounts for light from all sources as it is transmitted throughout the environment Local illumination only accounts for light that directly hits a surface and is transmitted to the eye

Direct and Indirect Light

Global Illumination II

Lighting/Illumination Color is a function of how light reflects from surfaces to the eye Global illumination accounts for light from all sources as it is transmitted throughout the environment Local illumination only accounts for light that directly hits a surface and is transmitted to the eye

Light Sources Any object emitting radiant energy is a light source that contributes to the lighting effects for other objects in a scene Point light sources: defined by its position and the color of the mitted light (RGB) Infinitely distant light sources: basically a point light source very far from a scene. Defined by its direction and the color of the light (RGB)

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency. Reflected light?

Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency. Reflected light? This depends on the surface property!

Types of Reflection Functions Ideal Specular  Reflection Law  Mirror

Types of Reflection Functions Ideal Specular  Reflection Law  Mirror Ideal Diffuse  Lambert’s Law  Matte

Types of Reflection Functions Ideal Specular  Reflection Law  Mirror Ideal Diffuse  Lambert’s Law  Matte Specular  Glossy  Directional diffuse

Materials PlasticMetalMatte From Apodaca and Gritz, Advanced RenderMan

Illumination Model Ambient Light  Uniform light caused by secondary reflections Diffuse Light  Light scattered equally in all directions Specular Light  Highlights on shiny surfaces

Ambient Light A =intensity of ambient light k a =ambient reflection coefficient Really 3 equations! (Red, Green, Blue) Accounts for indirect illumination Determines color of shadows A=R*C r + G*C g +B*C b

Total Illumination

Diffuse Light Assumes that light is reflected equally in all directions Handles both local and infinite light sources  Infinite distance: L doesn’t change  Finite distance: must calculate L for each point on surface Surface

Diffuse Light C = intensity of point light source k d = diffuse reflection coefficient = angle between normal and direction to light Surface C=R*C r + G*C g +B*C b

The reflected luminous intensity observed from an ideal diffusely reflecting surface is proportional to the cosine of the angle between the direction of the incident light and the surface normal Lambert’s Law Surface

Lambert’s Law Surface Beam of Light

Lambert’s Law Surface Beam of Light The intensity of the received light:

Lambert’s Law Surface Beam of Light The intensity of the received light:

Diffuse Light Where is the light source?

Diffuse Light Where is the light source?

Total Illumination

Materials PlasticMetalMatte From Apodaca and Gritz, Advanced RenderMan

Specular Light Perfect, mirror-like reflection of light from surface Forms highlights on shiny objects (metal, plastic) Surface

Specular Light C =intensity of point light source k s =specular reflection coefficient =angle between reflected vector (R) and eye (E) n =specular coefficient Surface

Finding the Reflected Vector Surface

Finding the Reflected Vector Surface

Finding the Reflected Vector Surface

Finding the Reflected Vector Surface

Finding the Reflected Vector Surface

Finding the Reflected Vector Surface

Total Illumination

Multiple Light Sources Only one ambient term no matter how many lights Light is additive; add contribution of multiple lights (diffuse/specular components)

Total Illumination

Other Lights Attenuation caused by fog, smoke Spot lights

Attenuation Decrease intensity with distance from light

Attenuation Decrease intensity with distance from light d = distance to light r = radius of attenuation for light

Attenuation Decrease intensity with distance from light d = distance to light r = radius of attenuation for light

Without Attenuation

With Attenuation

Spot Lights Eliminate light contribution outside of a cone How to create spot lights ?

Spot Lights Eliminate light contribution outside of a cone Surface Zero! If outside of the cone

Spot Lights Eliminate light contribution outside of a cone Surface Depends on the angle β β If inside the cone

Spot Lights Eliminate light contribution outside of a cone Surface cosββ

Without Spot Lights

With Spot Lights

Implementation Considerations Surface >90: no contributions

Implementation Considerations Typically choose Clamp each color component to [0,1]

Opengl Functions See section how to set up light sources (light source pos - light source position and type - light source colors - radial-intensity attenuation - spotlights how to specify global lighting parameters how to specify surface properties

Next Lecture Shading Texture mapping & others Readings: HB 17-10, 18-1, 18-2 and 18-3