Computer Graphics Primer

1
Computer Graphics Primer

• Jyun-Ming Chen

2
Contents

• Rendering
• Light and Shading
• Phong and Gouraud Shading
• Texture Mapping
• Hidden Surface Removal
• Color Models (HSB, RGB, )

3
Rendering

• The computation required to convert 3D scene to
  2D display photo-realistically

4
Shading

• the gradation (of color) that give the 2D images
  the appearance of being 3D
• light-material interaction
• specular, diffuse, translucent

5
Light

• point, spot, distance lights
• ambient light to account for uniform level room
  lighting
• describe a light source through a three-component
  (RGB) intensity

6
Phong Illumination Model

• L light source property R reflection property
• ambient reflection
• diffuse reflection
• specular reflection (more later)
• final result

7
Phong Model (cont)

• For multiple light sources

• More on Specular

a?
8
Shading Modes

• Flat vs. Smooth
• Flat single color per face
• Gouraud (intensity interpolation)
• Phong (normal interpolation)

• Local vs. Global

9
Gouraud and Phong

• Most h/w implement Gouraud shading
• Phong shading can better imitate specular
  effects (?normals are interpolated)

10
Texture Mapping

• A way to render realistic picture w/o using too
  many polygons

11
Texture Coordinate System

• Texture a 2D array of color values, each unit is
  called texel
• Every texture map has (s,t) coordinates 0,0 to
  1,1
• Each vertex in a polygon specifies its texture
  coordinates (s,t), then map to the given image to
  determine the corresponding texture

12
Example
13
Example
14
HSR (Hidden Surface Removal)

• Painters algorithm
• Depth-sorting Back-to-front rendering
• Sort based on some points on the polygon
• Problem can not resolve this

15
HSR (cont)

• Z-buffer Algorithm
• For each pixel, we keep track of the
  corresponding depth or distance.
• This is called the z-buffer.
• If a new object is drawn, only replace the pixels
  in the frame-buffer if the new pixels value is
  less than the pixels value in the z-buffer.

16
Color Models (Ref from Adobe)

• RGB
• additive color

• CMY
• subtractive colors

17
Color Models (cont)

• HSB
• Hue defines the color from Red-Green-Blue
• Saturation how the hue differs from natural grey
• Brightness the level of illumination