University of North Carolina

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Chapter 1 Graphics Systems and Models

• Overview of semester
• (more or less)

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Announcements

• Anyone having troubles re Hurricane Katrina?
• Prequiz questions?
• New people need forms?

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Computer Graphics System

• Creating and manipulating 2D images
• One of few subjects in Computer Science where YOU
  interface with the user in easy ways

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Pixels and the Frame Buffer I

• Most current systems are raster
• Old systems could be vector
• This leads to a pixilated world

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Pixels and the Frame Buffer II

• The Frame Buffer is a special piece of memory set
  aside to store per pixel information about images
• On most modern machines, this is a separate piece
  of memory on the Graphics Card (GPU) and it
  stores 32 bits
• RGBA

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Output Devices I

• Cathode-ray Tubes (CRT)

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Output Devices II

• Vector Devices
• The ray drew uninterrupted lines from a start
  position to an end position
• Did anyone here use LOGO in elementary school?
• Positives
• Smooth lines/curves
• Negatives
• Hard to draw a full image
• Two values ON/OFF

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Output Devices III

• Modern use Oscilloscope

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Output Devices IV

• Pen plotter
• Old style Printer

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Output Devices V

• Shadow-mask CRT
• AKA color TV, modern computer monitor

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Output Devices VI

• Interlaced v. Non-interlaced
• TV screen v. Computer Monitor
• Interlacing fools the eye into thinking that the
  refresh rate is doubled

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Output Devices VII

• Flat-panel technologies

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Output Devices VIII

• The wires on the outside set the (X, Y)
  coordinate for the pixel to be set
• LED
• Middle panel has Light Emitting Diodes
• LCD
• Controls polarization of liquid crystals
• Plasma
• Excitable gases turn into glowing plasma

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Output Devices IX

• Which is better?
• Plasma has better color and intensity
• Plasma has quicker burn in
• LCDs never burn in
• LCDs have a lower maximum resolution
• LED is promising but still maturing
• CRTs are BIG
• CRTs are on their way out

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Creating Images

• Visible Light

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Human Visual System I

• We need to fool the human eye
• How does the eye function?

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Human Visual System II

• Rods
• Intensity only
• Essentially night vision and peripheral vision
  only
• Since we are trying to fool the center of field
  of view of human eye (under well lit conditions)
  we ignore rods

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Human Visual System III

• Cones
• Three types perceive different portions of the
  visible light spectrum

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Human Visual System IV

• Because there are only 3 types of cones in human
  eyes, we only need 3 stimulus values to fool the
  human eye
• Note Chickens have 4 types of cones

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Imaging Systems I

• Make a camera that acts similar to the human eye

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Imaging Systems II

• Field of View
• In Humans, its limited to the spread of the
  cones at the back of the eye, the diameter of the
  eye and the shape of the lens
• In pinhole cameras, its limited to the size of
  the back plane and distance from the pinhole to
  the back plane

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Imaging Systems III

• Note that the image is upside-down on the film
  (and retina)
• Since we make a synthetic camera, we can put the
  film in front of the camera and leave it
  right-side up
• Similar triangles

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Overview of (OpenGL) Graphics Programming
Drivers
You write this
Open GL
nVIDIA/ATI
GLUT/FLTK/Java
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Whats our job? (OpenGL)

• Objects
• Where they are
• What material properties they have
• Lights
• Where they are
• Attributes they have
• Viewer
• Location
• Which direction he faces
• Field of view, etc.

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Modeling v. Rendering
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Graphics Hardware I

• Parallelism
• The modern CPU is (generally) a single thread,
  one instruction on one input
• The graphics problem is highly parallelizable
• Each triangle that does not overlap is
  independent
• Each final fragment is independent of its
  neighbors

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Graphics Hardware II

• This is the reason for a separate GPU
• Also allows a separate piece of hardware to worry
  about screen refreshing

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Rasterization

• Geometry v. Image

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Graphics Hardware III

• 1) Manipulation of vertices (geometry)
• First job of a GPU
• Transform vertex location (3D?2D)
• Interaction between light and vertex (color)
• 2) Manipulation of fragments (pixels)
• Last job of GPU
• Is this fragment visible?
• Does it receive a texture?
• Performance of both parts reported as part of
  rendering speed

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Class Schedule I

• Just finished Chapter 1
• OpenGL and UIs
• Chapter 2 Getting started with 2D coding
• 1 week
• Chapter 3 Interactive user input
• 1 week

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Class Schedule II

• Chapter 4 Geometry and Math in Graphics
• 1.5 weeks
• Chapter 5 Camera location and viewing (3D)
• 1 week
• Chapter 6 Getting the color right
• 1.5 weeks

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Class Schedule III

• Chapter 7 What the hardware does I
• 1.5 weeks
• Chapter 8 What the hardware does II
• 1 week
• This is where the overview begins
• Chapter 9 Programming GPUs
• 1 week

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Class Schedule IV

• Chapter 11 CAGD Graphics of Design
• 1 week
• Chapter 12 Ray-tracing and other advanced
  rendering
• 1 week
• Chapter 10 Modeling
• If we get to it

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Questions?