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Computer Graphics

Week3 –Graphics & Image Processing

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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Pixels

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A Graphics System

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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

7CRT (Cathode-ray tube)

Output Devices

• 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

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Joystick Data tablet Anything else?

Hand Foot Voice Mind?

Images: Physical and Synthetic

• Image formation– Lighting– Shading– Properties of materials

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Objects and Viewers

• 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

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Objects and Viewers

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3D world 2D image

Light and Images

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Synthetic-camera Model

Film Plane

Projection Plane

Single Point Light Source

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Ray Tracing

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Penetrating transparent surfaces Reflected by

Mirrors Diffuse surfaces

Refracted Absorbed

Human Visual System

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Visual system does not have the same response to each color.We are most sensitive to green light

Pinhole Camera

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Pinhole Camera

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dz

xx

dz

yy

p

p

/

/

d

h

2tan2 1

(xp, yp, -d) is the projection of (x, y, z)

Synthetic-camera Model

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Bellows Camera Projector

Synthetic-camera Model

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COP(Center of Projection)

Focal Length

Synthetic-camera Model

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Film Plane

Projection Plane

Synthetic-camera Model

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Clipping Window

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

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Example: Scene graph

Graphics Architecture

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Early graphics system

Computeline segments

Drawline segments

Very high rate to avoid flickering

Graphics Architecture

36Display-processor architecture

Graphics Architecture

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Arithmetic pipeline: doubling the throughput!

Pipeline Architecture: Geometric pipeline

Pipelining

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Arithmetic pipeline: doubling the throughput!

Pipeline Architecture: Geometric pipeline

Geometric Pipeline

• Transformation– Conversion between coordinate systems– Translation, rotation, scaling– Aggregate transforms by matrix multiplications

• Clipping– Could be further pipelined

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Geometric Pipeline

• 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 Lecture 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

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