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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