Computer Graphics

Lecture 1 - Computer Graphics Background

History

1950s

Sage Air Defence System  (Semi Automatic Ground Environment)  

• Built by IBM for the Air Force in the 1950s
• Used computers to track aircraft and displayed radar blips on computer graphic consoles as interactive vector graphics
• One of the first applications of computer graphics to track enemy aircraft.

1960s

Sketchpad

• IBM, Sperry-Rand, Burroughs and a few other computer companies existed
• Computers  had a few kilobytes of memory, no operating systems to speak of and no graphical display monitors
• Peripherals were Hollerith punch cards, line printers, and roll-paper plotters. 
• Only programming languages supported were assembler, FORTRAN, and Algol
• Function graphs and ``Snoopy'' calendars were about the only graphics done.

• 1963 - Ivan Sutherland presented his paper Sketchpad at the Summer Joint Computer Conference
• Sketchpad allowed interactive design on a vector graphics display monitor with a light pen input device
• True origins of computer graphics

Software and Algorithms

• Jack Bresenham draws lines on a raster device
•  Anti-aliased lines and curve drawing is a major topic in computer graphics. 
• Steve Coons introduced parametric surfaces and developed early computer aided geometric design concepts. 
• Work of Pierre Bézier on parametric curves and surfaces also became public. 
• Author Appel at IBM developed hidden surface and shadow algorithms that were pre-cursors to ray tracing. 

Hardware and Technology

• Doug Englebart invented the mouse at Xerox PARC. 
• Evans & Sutherland Corporation and General Electric build flight simulators with real-time raster graphics

Early '70's

• State-of-the-art computer was:
• IBM 360 computer with about 64 KB of memory
• Tektronix 4014 storage tube or a vector display
• light pen 

Tektronix Display : 

• ability to be used as a terminal, linked to a server computer
• 64 Kb RAM
• Resident BASIC Interpreter
• Resident Graphics System (in BASIC)
• Expanded cartridge with signal processing libraries

Software and Algorithms

• Rendering (shading) devised by Gouraud and Phong at the University of Utah
• Phong also introduced a reflection model that included specular highlights
• Keyframe-based animation for 3-D graphics was demonstrated.
• Xerox PARC developed a "paint'' program.
• Ed Catmull introduced parametric patch rendering, the z-buffer algorithm, and texture mapping.

Hardware and Technology

• Evans & Sutherland Picture System:
• high-end graphics computer
• vector display with hardware support for clipping and perspective
• Xerox PARC introduced the Altos personal computer

Mid to Late '70's

Software and Algorithms

• Turned Whitted developed recursive ray tracing,which became the standard for photorealism 

Hardware and Technology

• The Apple I and II computers became the first commercial successes for personal computing
• DEC VAX computer was the mainframe (mini) computer of choice.
• Arcade games such as Pong and Pac Mac became popular.
• Laser printers were invented at Xerox PARC.

Early '80's

Hardware and Technology

• Xerox Star Introduced - GUI developed
• IBM PC  marketed in 1981 
• Apple MacIntosh started production in 1984
• Computers with a mouse, bitmapped (raster) display, and Ethernet became the standard in academic settings

Xerox Star                                                Apple Lisa

Middle to Late '80's

Software and Algorithms

• Jim Blinn introduces blobby models and texture mapping concepts. 
• Binary space partitioning (BSP) trees introduced as a data structure
• Loren Carpenter starting exploring fractals in computer graphics
• Postscript was developed by John Warnock and Adobe was formed. 
• Steve Cook introduced stochastic sampling to ray tracing
• Character animation became the goal for animators
• Radiosity introduced by Greenberg at Cornell. 
• Photoshop was marketed by Adobe. 
• Video arcade games took of
• Desktop publishing begins. 
• Unix with X windows was the platform of choice

Hardware and Technology

• Sun workstations, with the Motorola 680x0 chipset became popular as advanced workstation
• Video Graphics Array (VGA) card was invented at IBM
• Silicon Graphics (SGI) workstations supported real-time raster line drawing and later polygons became the computer graphics standard. 
• Data glove, a precursor to virtual reality, was invented at NASA
• VLSI for special purpose graphics processors and parallel processing became hot research areas.

Early '90's

• SGI workstation with at least 16 MB of memory a must-have computer:
• 24-bit raster display
• hardware support for Gouraud shading
• z-buffering for hidden surface removal
• Laser printers and single frame video recorders were standard.
• Unix, X and Silicon Graphics GL were the operating systems, window system and application programming interface (API)
• Shaded raster graphics introduced in motion pictures.

Software and Algorithms

• Mosaic, the first graphical Internet browser , written at the University of Illinois, National Center for Scientific Applications (NCSA). 
• MPEG standards for compressed video began to be promulgated.
• Dynamical systems (physically based modeling) that allowed animation with collisions, gravity, friction, and cause and effects were introduced. 
• In 1992 OpenGL became the standard for graphics APIs 
• In 1993,the World Wide Web took off. 
• Surface subdivision algorithms were rediscovered. 
• Wavelets begin to be used in computer graphics.

Hardware and Technology

• Intel 486 chipset gives PCs reasonable floating point performance 
• 1994 - Silicon Graphics produces the Reality Engine:  hardware for real-time texture mapping
• Ninetendo 64 game consoleprovides Reality Engine-like graphics for game players. 
• Scanners introduced.

Middle to Late '90's

• PC market erupts and supercomputers  wane
• SGI collapses and startups entergraphics field.

Software and Algorithms

• Image based rendering becomes  area for research in photo-realistic graphics
• Linux and open source software become popular.

Hardware and Technology

• PC graphics cards,(e.g. 3dfx and Nvidia), introduced. 
• Pentium chipset makes PCs almost as powerful as workstations 
• Motion capture, begun with the data glove, becomes a primary method for generating animation sequences. 
• 3-D video games become very popular: DOOM (which uses BSP trees), Quake, Mario Brothers, etc. 
• Graphics effects in movies becomes pervasive: Terminator 2, Jurassic Park, Toy Story, Titanic, Star Wars I. V
• Virtual reality and the Virtual Reality Markup Language (VRML)  

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

35mm Camera	Focal Length(mm)	Angle of View (Degrees)
Extreme Telephoto	800	3.5
	400	6.0
	200	12.5
Moderate Telephoto	135	18.0
	85	29.0
	50	46.0
Normal	43	53.0
Moderate Wide Angle	24	84.0
Wide Angle	18	94.0

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

One-Pass                                                                 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