Rendering Methods

• Object Model

• Lighting Model

• Camera Model

Wireframe models                                                     Wireframe models with hidden lines

Ambient Illumination                                                                Faceted Shading

Gouraud Shading                                                                    Phong Shading

Phong Shading - Polygon Meshes                                    Phong Shading - Bicubic Patches

Advanced Illumination                                                            Texture Mapping

Bump Mapping                                                                            Reflection Mapping

 

Camera Model

Focal Lengths and Angles of View

Unit Cube at 5 units from image plane

Camera held fixed with different angles of view
(Extreme Wide Angle, Wide Angle, Normal, Telephoto)

Camera position adjusted maintaing constant image size
(Extreme Wide Angle, Wide Angle, Normal, Telephoto)
 

Hidden Surface

Object Space
    Painter's Algorithm - Depth Sort

Image Space
    z-buffer (depth buffer)

Illumination Model

Surfaces in real world environments receive light in 3 ways:

1. Directly from exisiting light sources such as the sun or a lit candle

2. Light that passes and refracts through transparent objects such as water or a glass vase

3. Light reflected, bounced, or diffused from other exisiting surfaces in the environment

Local (Simple)

Material Models

• ambient light

• diffuse light

• specular light

• Phong model

Simple Shading Model

• Objects under the influence of light

• Deficiencies

  • point light source

  • no interaction between objects

  • ad hoc, not based on model of light propagation

• Benefits

  • fast

  • acceptable results

  • hardware support

Ambient Light

Diffuse Reflection

• Light from the light source is sent in everyu direction

• Object appearance independent of viewer position

• Only depends on relative position of light source

Diffuse + Ambient

Specular

Perfect Reflector (Mirror)

Imperfect Reflector - Phong Model

Global

Ray Tracing

www.povray.org

Radiosity

Radiosity Method

• From field of thermal engineering to account for radiative heat transfer

• Foundation - conservation of radiative energy in a closed environment

• First applied to computer graphics in 1984 at Cornell and Hiroshima University

• Calculates lighting effects of ideal diffuse reflections

• Other rendering techniques use a directionless " ambient lighting "

Radiosity methods

• are three-dimensional object space algorithms that solve for intensities at disrcete points or areas on modeled surfaces, not for pixels on a 2D image plane.

• create solutions independent of camera location or orientation.

• make all surfaces capable of reflecting or emitting light energy

• Radiosity methods compute specular reflections and refractive transparencies as a second pass using ray-traced specular reflections and transparencies

Two-Pass

Radiosity Procedure

1. Modeled world is broken into a finite number of N discrete patches

2. Radiosity equation used to relate patches

3. N simultaneous equations solved iterartively using Gauss-Seidel method

4. The radiosity equation uses of the following:
    Energy that leaves Surface_A and strikes  Surface_B is attenuated by 2 factors:

• The physical relationship between Surface_A and Surface_B (known as the form factor).

• The reflectivity of Surface_A (some light will be absorbed and not reflected to Surface_B).

5. Form factors are dimensionless quantities that describe the radiative exchange between 2 surfaces based on the geometric relationship within their virtual environment