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Chapter 1: Graphics Systems and Models
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Applications of C. G. – 1/4 Display of information
Maps GIS (geographic information system) CT (computer tomography) MRI (magnetic resonance imaging) PET (positron-emission tomography) Fluid flow, molecular biology, mathematics
…
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Display of Information
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Applications of C. G. – 2/4 Design
CAD (computer-aided design): VLSI (very-large-scale integrated) circuits
Together with other tools:architecture or interior design
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Interior Design
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Applications of C. G. – 3/4 Simulation and animation
Flight simulation – pilot training Games and educational software Benefits:
Less cost Less danger, e.g. combination with the VR (virtual
reality) techniques can help surgical interns and astronauts
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Applications of C. G. – 4/4 User interfaces
Friendly working environment:windows, icons, menus, pointing devices
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A Graphics System
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Pixels
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Frame Buffer High-end systems: VRAM or DRAM Simpler systems: part of memory Depth: the number of bits per pixel True color: depth=24 Resolution: the number of pixels in the
frame buffer
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Rasterization or Scan-conversion Conversion of geometric entities to pixels
in the frame buffer High-end systems
Special-purpose processors
Simpler systems A single and shared processor
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Output Devices – 1/2
CRT (Cathode-ray tube)
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Output Devices – 2/2 CRT
Refresh: at least 50 times per second Interlace and non-interlace systems Color CRTs have three colored phosphors and a
shadow mask Other raster devices:
LCD (liquid-crystal displays) Plasma panels and digital projection systems Non-refreshable: printers and plotters
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Shadow-mask CRT
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Input Devices Mouse Joystick Data tablet Anything else?
Hand Foot Voice Mind?
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Images: Physical and Synthetic Image formation
Lighting Shading Properties of materials
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Objects and Viewers – 1/3 Object: formed from geometric primitives
Points, lines, polygons Vertex (pl. Vertices) is the most primitive one
Viewer: Locations Viewing angles
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Objects and Viewers – 2/3
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Objects and Viewers – 3/3
3D world 2D image
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Light and Images
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Electromagnetic Spectrum
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Single Point Light Source
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Ray Tracing Penetrating transparent surfaces
Reflected by
Mirrors
Diffuse surfaces
Refracted
Absorbed
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Human Visual System
Visual system does not have the same response to each color.We are most sensitive to green light
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Pinhole Camera – 1/2
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Pinhole Camera – 2/2
dz
xx
dz
yy
p
p
/
/
d
h
2tan2 1
(xp, yp, -d) is the projection of (x, y, z)
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Synthetic-camera Model – 1/4
Bellows Camera Projector
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Synthetic-camera Model – 2/4
COP(Center of Projection)
Focal Length
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Synthetic-camera Model – 3/4
Film Plane
Projection Plane
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Synthetic-camera Model – 4/4Clipping Window
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Programmer’s Interface
Interface for a painting program
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Application Programmer’s Interface
Specifications of the functions in the graphics library
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Three-dimensional APIs Objects Viewers Light sources Material properties
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Camera(Viewer) Specifications Position (COP) Orientation Focal length Film plane
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Sequence of Images Wireframe Flat shading
HSR (Hidden surface removal) Smooth shading Curves and surfaces
NURBS, Bezier curves/surfaces Texture mapping
Bump mapping, environmental maps, antialiasing…
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Wireframe
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Flat Shading
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Smooth Shading
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Modeling With Curves/surfaces
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Bump Mapping
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Environmental Maps
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Antialiasing
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Modeling-rendering Paradigm
Example: Scene graph
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Graphics Architecture – 1/3
Early graphics system
Computeline segments
Drawline segments
Very high rate to avoid flickering
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Graphics Architecture – 2/3
Display-processor architecture
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Graphics Architecture – 3/3
Arithmetic pipeline: doubling the throughput!
Pipeline Architecture: Geometric pipeline
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Geometric Pipeline – 1/2 Transformation
Conversion between coordinate systems Translation, rotation, scaling Aggregate transforms by matrix multiplications
Clipping Could be further pipelined
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Geometric Pipeline – 2/2 Projection
Remaining 3D objects are projected into 2D objects
Parallel or perspective projections Rasterization
Convert 2D objects into pixels
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Performance Characteristics Latency Throughput:
How fast we can move geometric entities through the pipeline
How many pixels per second we can alter in the frame buffer
Pipeline architecture is not a must Ray tracing or radiosity for better quality
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Summary & Notes of Chapter 1 Application of computer graphics A graphics system Human visual system Pinhole and synthetic camera models Image formation Geometric pipeline Realistic images may require resolution of up
to 40006000