Welcome to CSc 830 Advanced Computer Graphics

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Welcome toCSc 830 Advanced Computer Graphics

• By Ilmi Yoon

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What does this course cover...

• Computer Graphics is fun!!!!
• Think about all the movies with spectacular
  computer graphics special effect.
• But we are not artists. We are the ones who makes
  artists dream and imaginations come true!!!!
• So, you are not learning how to use tools like
  AutoCAD, 3D studio MAX, Abobe Photoshop, Maya,
  etc

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You will learn

• Concepts of 3D modeling Simulations
• Animation
• But most importantly RENDERING of 3D graphics
  which is the fundamental for the others.
• Topics (check the syllabus)

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Graphics Applications

• Entertainment Cinema

Universal Jurassic Park
Pixar Geris Game
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Graphics Applications

• Entertainment Games

id Quake II
Cyan Riven
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Graphics Applications

• Medical Visualization

The Visible Human Project
MIT Image-Guided Surgery Project
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Graphics Applications

• Computer Aided Design (CAD)

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Graphics Applications

• Scientific Visualization

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Survey on your CG related background

• Basic Concept (Transformation, Camera,
  Projection, Rendering, Shading)
• Software Tools (3D Studio Max, Maya, Alias,
  Director, VRML)
• Library (OpenGL, Open Inventor, Renderman,
  directX, Java3D)
• Advanced Issues (Animation, Rendering
  Acceleration, Geometry Compression, Global
  Illumination, Simulation, IBR)

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My Current Research Topics

• Webs on the Web - 3D Visualization of
  bioinformatics data through the WWW
• The Virtual Tour Project - The virtual tour
  through the WWW
• Scientific Visualization - Remote rendering of
  huge simulation data sets (LBL intern position)
• 3D modeling tools for biologists
• Web-based hydrodynamics computing
• Automated Behavioral Phenotype Detection and
  Analysis Using Color-Based Motion Tracking

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Modeling and Animation using Blender

• Why Blender?
• Use Gmax if you want
• Why using modeling and animation tools?
• Tlaloc.sfsu.edu/yoon/csc830/Assign0.html

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Basic Rendering Pipeline
ViewingTransformation (WS -gt CS)
Modeling Transformation (OS -gt WS)
Visibility Culling
Database of 3D models
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Geometric/Modeling Transformation

• Goal specify objects position and orientations
  in a 3D world
• Use Linear transformations that rotate and
  translate objects vertices.
• Apply these transformations in matrix form

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Modeling Transformation

Viewing Transformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Database of 3D models
3D models defined in their own model space or
object space(OS) - Modeling of an object that
consists of multiple object parts use a
hierarchical structure of this modeling
transformations. Modeling transformations
orient models within a common coordinate system
called world space (WS) - multiple objects in a
space All objects, lights, and camera (viewer)
is in one world space
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Rigid-Body Transformation

• Euclidean transformation
• Preserve the shape of the objects that they act
  on
• Includes rotations and translations

rotation
translation
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Homogeneous Coordinate System

• Rotation multiplies and translation adds
• causes distingtion for every single calculation
• Homogeneous system treats translation and
  rotation same by extending one dimension
• Repeating usages, scale, skew are also fine

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Viewing

• Goal map the visible part of a 3D world to a 2 D
  image
• Use camera-like parameters to define a 3D view
  volume
• Project the view voulme onto a 2D image plane
• Map viewport on the image plane to the screen

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Viewing Transformation

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Another change of coordinate systems Maps
points from world space into eye (camera) space
Eye position becomes the origin and viewing
direction is oriented along some axis (z/-z)
eye
World space
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Viewing transformation

• Same with other transformation (rotation
  translation)
• Specially treated because camera position
  viewing direction defines it.

eye
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Visibility Culling

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Database of 3D models
Viewing volume is defined. Objects outside
viewing volume is not visible. This process
can contribute substantial performance
improvement and there are many number of
techniques.
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Clipping

• Goal cut off the part of objects outside the
  view volume to avoid rendering them

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Illumination

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Illumination needs to be done before projection
since Z value does matter for shading
calculation Shading usually refers local
illumination calculated based on surface
material, surface normal, view direction, and
light source Texture map can be added here
Global illumination adds interaction between
objects, reflection, refration, BRDF, etc
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Lighting, Shading

• Lighting and shading give objects shape
• Important effects
• shading
• shiny highlights
• reflections
• shadows
• Local techniques simplify these effects to
  improve performance

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Shading

• A reflection (diffuse specular florescence)
  model describes the interaction of light with a
  surface, in terms of the properties of the
  surface and the nature of the incident light.
• Surface surface normal material (combination
  of ka, kd, ks and n)
• I Iaka Iikd(LN) ks (RV)n/(rk)

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Global illumination

• Global techniques provide more accuracy by
  simulating light propagation among all surfaces
  in a 3D world.
• Local shading (Gauroud shading, Phong shading)
  does not calculate global effect (shadow,
  reflection, refraction, scattering, etc)
• Technique
• ray tracing
• radiosity

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Projection

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Another transformation from camera space to
image space
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Projection

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Another transformation from camera space to
image space Z value is used to calculate
ratio of x y and then discarded (right after Z
buffer comparison)
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(Perspective) Projection

• The projection maps all of out 3D coordinates
  onto our desired viewing plane, thus making 3D
  world into an image

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Rasterization, Clipping, Display

ViewingTransformation (WS -gt CS)
Projection
Illumination
Rasterization Clipping Display
Visibility Culling
Modeling Transformation (OS -gt WS)
Final transformation from image space to
viewport coordinates Filling pixels Z buffer
(Closer objects over write farther objects)
Clipping cuts off objects outside of viewport
2D operation (filling a triangle properly)
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Scan Conversion

• Goal convert a project, clipped object into
  pixels on raster lines.
• Use efficient incremental methods

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Antialiasing

• Raster displays produce blocky aliasing artifacts
• Antialiasing techniques reduces the problem by
  applying the theory of sampling and signal
  processing

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Texture (map)

• Blinn, 1978
• Texture mapping is the process of transforming a
  texture onto the surface of a three-dimensional
  object.
• Makes object realistic appearance, but increasing
  the overall size of object (problem when
  transmitted)
• Bump mapping

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Other issues

• Rendering acceleration (rasterization, texture
  map, spacial subdivision, collision detection,
  progressive rendering, view dependent rendering,
  image-based rendering,)
• Anti-aliasing
• Physically based simulation

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Project 1

• What is OpenGL? Mostly recognized graphics
  library
• You are using OpenGL Glut only for displaying
  purpose for project 1 project 4.
• For term project, you may rewrite your project 1
  4 using OpenGL and then add animations on top
  of it.

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OpenGL

• OpenGL is strictly defined as a software
  interface to graphics hardware.
• It is a 3D graphics and modeling library
• variety purposes, CAD engineering, architectural
  applications, computer-generated dianosaurs in
  blockbuster movies
• Developed by SGI

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OpenGL Library Organization
GLU
Frame Buffer
GL
OpenGL Application Program
Xlib,Xtk
GLUT
GLX
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Color

• Various color spaces provide ways to specify
  colors in term of components
• red, green, blue
• hue, saturation, value
• Different output devices display different
  subsets of the perceptible colors

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RGB Color

• Conceptually, there are separate frame buffers
  for red, green, and blue
• Each pixel has separate red, green, and blue
  components that corresponding to location in
  memory
• Typical system might be a 1028x1024 array of
  pixels, each pixel might consist of 24 bits (3
  bytes)

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RGB Color (cont)

• Example
• in a 24 bits example, there are 224 possible
  colors which sometime refered to as 16M colors
• How much frambuffer we need for a 1280x1024
  pixels?

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Color in OpenGL

• glColor3f(1.0,0.0,0.0)
• this present a red color
• 3f use a RGB model, and the value of the
  component is float in C.

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• Four-color(RGBA) system
• A is called alpha channel, stored in the frame
  buffer as are the RGB value
• The alpha value will be treated by OpenGL as an
  opacity or transparency
• glClearColor(1.0, 1.0, 1.0, 1.0)
• solid and white

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Indexed Color

• What happen if the size of frame buffer is not
  enough,relatively to a spatial resolution given?
• Many systems have frame buffers that are limited
  in depth.
• We can select colors by interpreting our
  limited-depth pixels as indicies rather than as
  color values

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Color-lookup Table

• Suppose frame buffer has k bits / pixel
• Each pixel value or index is an integer between 0
  and 2k-1
• Suppose we can display colors with an accuracy of
  m bits
• ex k m 8, we can choose 256 colors out of 16M

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Color-lookup Table

• Input Red Green Blue
• 0 0 0 0
• 1 2m-1 0 0
• 2 0 2m-1 0
• 2k-1

m bits
m bits
m bits
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Indexed Color
Color Lookup Table
Red
A
A
Green
Color Lookup Table
Blue
Color Lookup Table
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For your inspiration.

• Electronic theater Siggraph 2001.