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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
42
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