Topic 5 Concept of Computer Graphics

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Topic 5 Concept of Computer Graphics

• Introduction
• Output Primitives and Attributes
• Two dimensional Viewing
• Graphical User Interfaces
• Three Dimensional Concepts
• Three Dimensional Display in Nuclear Medicine

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Computer Graphics

• Everything on computers that is not text or
  sound.
• Computer graphics as drawing pictures on
  computers.
• Nuclear Medicine uses computer graphics to
  display images

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Graphic Software

• General Programming Package (Graphic Library in C
  etc)
• Application Package (For None-programmer)
• Modelling TransformationgtWorld
  CoordinatesgtNormalised Coordinates

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User Graphic Interface

• Consist of windows, pull-down and pop-up menus,
  icons, pointing device.
• Popular graphic user interface X windows, MS
  windows, Macintosh, OpenLook and Motif
• Graphic package Specialised interactive dialogue
• General Graphic Package interface to standard
  window system PHIGS for X windows.

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User Graphic Interface
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Output Attributes
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Transformation Pipeline
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Display Processor in Graphic System
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From Object Model to Display Device
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Object Rendering
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Basic Building Blocks For Pictures

• Output Primitives
• Characters,
• Geometric Entities.
• Lines,
• Filled Areas,
• Colours
• Polygons

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Output Primitives -Lines and Points
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Output Primitives - Circles
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Output Primitives - Polygon
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Properties of the Output Primitives

• How it is displayed
• Intensity
• Colour
• Style
• Pattern

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Geometric Transformation

• Change size, position or orientation
• translation
• rotation
• scaling
• Altering or Manipulating Display

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Transformations
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Transformations
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Two Dimensional Viewing

• Specify which part of the picture
• which part of the picture
• where to put the picture
• Algorithms
• Point Clipping
• Line Clipping
• Polygon Clipping
• Text Clipping

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Two Dimensional Viewing
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3D Object Representation

• Object Boundaries
• Plane,
• Curved Surfaces
• Object Interiors
• Solid Objects
• Boundary Representation
• Space-partition Representation

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3D Object Representation
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3D Transformation

• Transformation
• translation, rotation, scaling
• Rotation in 3D
• a composite of 3 rotations
• X-axis rotation

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3D Transformation
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3D Display

• View an object from any spatial position front,
  top etc.
• Projection onto a flat viewing surface.

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3D Display
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Projection

• Specify a view plane
• Projections
• Parallel
• Perspective
• Projection transformation
• Clipping

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Parallel Projection
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Perspective Projection
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Different Viewing Directions
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Changing of Reference Point
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3D Surface

• 3D Surface Detection
• Identify the visible surface
• example ray-casting method
• Depth Cueing
• the intensity of lines decreases from the front
  to the back of the object.

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3D Surface Detection
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Depth Cueing
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Types of Depth Cues

• Stereoscopic display (different image for
  different eye)
• Hidden lines/surface removal
• Depth weighting (less intensity for distant
  object)
• Illumination (surface lighting)
• Rotation (cine loops)

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Surface Illumination

• Surface illumination
• the intensity of light that we should see.
• Surface rendering algorithm
• calculation of the light based on physical laws.
• Radiosity algorithm based on the propagation of
  radiant energy between the surface and the source.

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Surface Illumination
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Shading Techniques
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Reflection and Transparency
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Radiosity
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Lighting Conditions
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Colours in Computer Graphics
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Colour Models

• Colour Model
• The method for explaining the properties or
  behaviour of colour within some particular
  context.
• RGB Model
• based on tristimulus theory

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Colour Models
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Grey Scale
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Logarithmic Exponential
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Colour Translation
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Pseudo Colour Display
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True Colour Display
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3D Display in Nuclear Medicine

• Slice-and-Dice Display
• orthogonal slices, oblique slices
• Ray Tracing Volume Rendering
• - summed projection, maximum activity projection,
  volumeric compositing.
• Surface Rendering
• polygon tiling, binary voxel rendering.
• Mapping
• Bulls eye, cylindrical display

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Slice-and-Dice
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Ray Tracing
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Surface Rendering
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Volume Rendering
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Bulls Eye Mapping
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Clinical Applications in Nuclear Medicine

• Hot Spot Imaging
• Volume rendering with maximum activity projection
• Cardiac Imaging
• Perfusion imaging(Bulls eye), surface rendering
  with colour.
• Functional imaging (oxygen consumption),
  colouring blood-pool surface.
• Gated Blood Pool Studies cine display, surface
  rendering, maximum activity projection.
• Brains.