Download What is Computer Graphics? What is Image Processing?

What is Computer Graphics?
• Computer graphics is commonly understood to mean the
creation, storage and manipulation of models and images.
• Such models come from a diverse and expanding set of
fields including physical, mathematical, artistic, biological,
and even conceptual (abstract) structures.
• The term “computer graphics” was coined in 1960 by
William Fetter to describe new design methods he was
pursuing at Boeing.
• He created a series of widely reproduced images on a
plotter exploring cockpit design using a 3D model of a
human body.
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What is Image Processing?
• Image processing is the analysis of scenes or
reconstruction of model of 2D or 3D objects from their
pictures.
• Simple image processing can be used in CG to help
synthesize the image of a model.
• Also combining and transforming synthetic images
depends largely on image processing operations.
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What is Interactive Computer Graphics?(1/2)
• User controls contents, structure and appearance of
objects and their displayed images via rapid visual
feedback.
• Basic components of an interactive graphics system
– Input (mouse, tablet and stylus, joystick, scanner)
– Processing and storage
– Display/Output (screen, paper-based printer, video recorder)
• Batch mode has been used since 1950’s
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What is Interactive Computer Graphics?(2/2)
• First truly interactive graphics system, Sketchpad,
pioneered at MIT by Ivan Sutherland for his 1963 Ph.D.
thesis.
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Three Big Topics: Form, Behavior, Appearance
• Modeling: how to represent objects; how to build those
representations
• Animation: representing/controlling the way things move
• Rendering: how to simulate the image forming process
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Modeling
• How to represent real environment
– geometry: modeling surfaces, volumes
– photometry: light, color, reflactance
• How to build these representations
– declaratively: write it down
– interactively: sculpt it
– programmatically: let it grow
– via 3D sensing: scan it in
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Animation
• Model how things move
• How to represent motion
– sequence of stills, parameter curves
• How to specify motion
– by hand: tweak it until it looks right
– rule-based behaviors: artificial life
– physics: simulate Newton’s law
– motion capture: act it out yourself
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Rendering
• What’s an image?
– Distribution of light energy on 2D “film”: E(x, y, L, t) (L is
wavelength)
• How do we represent and store images
– sampled array of “pixels” : I(x,y)
• How to generate images from scenes
– input: 3D description of scene, camera
– solve light transport through environment
– project to camera’s viewpoint
– ray tracing
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Hot Application Areas
• Special effects
• Feauture animation
• PC graphics boards
• Virtual environments/games
• Visualization (science, architecture, space, etc.)
• The web
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Hot Research Topics
• Modeling
– getting models from the real world
• Animation
– physically based modeling
– motion capture
• Rendering
– more realistic: image-based modeling
– less realistic: impressionist, pen & ink
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Evolution: Graphics in Context
• Graphics has been a key enabling technology in the
evolution of computing environments:
– graphical user interfaces, visual computing, e.g., desktop
publishing, scientific visualization, information visualization
• Hardware revolution drives everything:
– every 12-18 months, computer power improves by factor of
2 in price/performance – Moore’s Law
– graphics memory and network speeds are on even faster
exponentials
• Graphics chips have major improvements every six to nine
months (e.g. Sony Playstation 2, nVidia GeForce 2, Nintendo)
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Evolution: Character Display (1960s - now)
• Display: text plus alphamosaic pseudo-graphics
• Object and command specification: command-line
typing
• Control over appearance: coding for text formatting
• Application control: single task
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Evolution: Vector Displays (1963 - 1980s)
• Display: line drawings and stroke text; 2D and 3D
transformation hardware
• Object and command specification: command-line
typing, function keys, menus
• Control over appearance: pseudo WYSIWYG
• Application control: single or multitasked, host-satellite
distributed computing
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Evolution: 2D bitmap raster displays for PCs and
workstations (1972 at XEROX - now)
• Display: windows, icons, legible text and “flat earth”
graphics
• Object and command specification: minimum typing
via WIMP (Windows, Icons, Menus, Pointer) GUI
(Graphical User Interface): point-and-click selection of
menu items and objects, etc.
• Control over appearance: real WYSIWYG
• Application control: multi-tasking, networked
client-server computation and window management
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Evolution: 3D graphics workstations
(1984 at SGI - now)
• Display: real-time, pseudo-realistic images of 3D scenes
• Object and command specification: 2D, 3D and nD
input devices and force feedback haptic devices for
point-and-click, etc.
• Control over appearance: WYSIWYG
• Application control: multi-tasking, networked
client-server computation and window management
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Evolution: Classic time-sharing is dead
• PCs and workstations merging in distributed
heterogeneous computer networks (e.g. LANs, WANs,
Internet)
• But file-, print- and compute-servers and network are
shared
• Client/Server computing, component software
technologies are dominant paradigms
• NC’s (Network Computers), thin clients attached to
powerful servers reprise dumb terminals and provide
central control
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New Forms of Computing: 1990s -(1/2)
• Multimedia:
text and graphics synchronized with sound and video
• Hypermedia:
multimedia with links (also called Interactive Multimedia)
• “Digital Convergence”:
merging of digital television and distributed
computing, consumer electronics: set-top computers (e.g., for Interactive TV,
Video-On-Demand)
• The Internet and Internet appliances
• Embedded computing
(information appliances, Personal Digital
Assistants)
• Immersive Virtual Reality:
desktop (“fishtank”) VR, immersive VR (via
Head-mounted Displays, Cave (180 George St.), Responsive Workbench),
augmented VR (via video see-through optics)
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New Forms of Computing: 1990s -(2/2)
• New Interaction technology
– Inexpensive interaction devices from research lab into marketplace
(makes 2D and 3D graphics no longer “special”)
– 3D (even time-varying, “4D”) interactive illustrations as clip art/clip
models coming soon
– Kids using computer graphics in gaming consoles; VR games and
rides with HMD and force-feedback input devices
• New forms of user-interface
– 3D Widgets; gestures-based; VR demands new interaction
technology
– Social interfaces (Microsoft’s Bob bombed)
– Agents/knowbots for indirect control
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Powerful, Inexpensive Processing
• Chips are Key in graphics subsystems
– Advances driven by Moore’s Law Price/performance improves 2x every 18
months due to doubling of number of transistors (Only exponential in
technology except growth of WWW)
• CPU
– Intel Pentium III, AMD Athlon, IBM/Motorola PowerPC, Sun UltraSPARC,
MIPS Technologies MIPS, Compaq Alpha, Hewlett Packard HPPA, IBM
POWER, SGI/Cray vector processors
• Graphics subsystems
– Chip vendors for games and set-top boxes, and for PC boards
– Sun’s VIS, Intel’s MMX/KNI, PowerPC’s Altivec, and AMD’s 3Dnow!
Instructions add multimedia support to main processor; in the future, 3D
graphics in every chip
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Chip Technology Advances in games & Graphics
Cards
•
New Game platforms and set-top boxes use high-end processors
(128-bit architectures, great graphics capabilities)
•
Nintendo N-Cube
•
Sega Dreamcast
•
Sony Playstation 2
•
3Dfx Voodoo5
•
nVidia GeForce 2
•
Significant advances in commodity graphics chips every 6 months,
outrunning CPU chip advances – Intel’s Pentium 4 chip due out this fall
has 42 million transistors, compared with only 26 million in the Pentium
III
•
Seriously threatening high-end workstations
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Application Distinctions: two basic paradigms(1/2)
• Sampled-based graphics: discrete samples are used to
describe visual information
– Pixels can be created by digitizing images, using a
samples-based painting program, etc.
– Often some aspect of the physical world is sampled for
visualization, e.g. temperature across Thailand
– Example programs: Adobe Photoshop, The GIMP (on UNIX)
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Application Distinctions: two basic paradigms(2/2)
• Geometry-based graphics: a geometrical model is
created, along with various attributes, and is then
sampled for visualization (this process is called
“rendering”)
– Often some aspect of the physical world is visually simulated
or “synthesized”
– Example 2D programs: Adobe Illustrator, Macromedia
Freehand, Corel CorelDraw, Microsoft PhotoDraw
– Example 3D programs: Alias/Wavefront Studio and Maya,
Avid’s SoftImage 3D, Autodesk’s AutoCAD and 3D StudioMax
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Sampled-based Graphics(1/2)
• Images are made up of a grid of discrete pixels for 2D
“picture elements”
• Pixels are point locations with associated sample values
usually of light intensity/colors, transparency, and other
control information
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Sampled-based Graphics(2/2)
• Samples can be created directly in a paint-type program
or as a result of sampling continuous (analog) visual
materials, e.g. a photograph can be sampled using many
devices including: flatbed and drum scanners, digital still
camera, frame grabbers
• Sample values can be input numerically (e.g. from database)
• Once an image is defined as a pixel-array, it can be
manipulated
– Image editing (cut & paste, using brush tools, etc.)
– Image processing (blurring, sharpening, rotating, etc.)
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Sampling an Image
• Lets do some sampling of an image of a building
• A color value is measured at every grid point
Note: this poor sampling creates “blocky image” when reconstructed
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What’s the Advantage?
• Once image is defined in terms of colors at (x,y) locations
on grid, we can change the image easily by altering
location or color values
• Two or more images can be combined
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What’s the Disadvantage?
• WYSIWYG (What You See Is What You Get): There is no
additional information
– No depth information
– can’t examine scene from a different point of view
– at most can play with the individual pixels or groups of
pixels to change colors, enhance contrast, find edges, etc.
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Examples of 2D Image Manipulation(1/2)
• There are Many things one can do with sampled images
(military, entertainment, art, design, medicine)
• Digitally enhanced images are more and more common
(magazines cover, etc.)
• Movies: A Bug’s Life, Babe, Titanic, Jurassic Park
• Photorealistic images
– no way to tell if news photos are “real” photographs
– photographic evidence no longer considered “proof”
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Examples of 2D Image Manipulation(2/2)
• Photography and painting are merging in the art of digital
imaging
Father, mother
and son, all at
3 years of age
• This course emphasizes geometry-based graphics
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Geometry-Based Graphics
• Geometry-based graphics applications store
mathematical descriptions or “models” of geometric elements
(lines, polygons, polyhedrons…) and their associated attributes
(color, material properties). These elements are primitive
geometric shapes (primitive for short).
• Images are created as pixels arrays (via sampling of the
geometry) for viewing, but are not store as part of the model.
Image of many different views can be generated from the same
model.
• Can’t work directly with the individual pixels
• The geometric elements are manipulated and redisplayed
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Composition of a Geometric Model
• Primitives are assembled to create the final object
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