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
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
Graphic Software
• General Programming Package (Graphic Library in C etc)
• Application Package (For None-programmer)
• Modelling Transformation=>World Coordinates=>Normalised Coordinates
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.
User Graphic Interface
Output Attributes
Transformation Pipeline
Display Processor in Graphic System
From Object Model to Display Device
Object Rendering
Basic Building Blocks For Pictures
• Output Primitives– Characters, – Geometric Entities.– Lines, – Filled Areas, – Colours– Polygons
Output Primitives -Lines and Points
Output Primitives - Circles
Output Primitives - Polygon
Properties of the Output Primitives
• How it is displayed:– Intensity– Colour– Style– Pattern
Geometric Transformation
• Change size, position or orientation:– translation– rotation– scaling
• Altering or Manipulating Display
Transformations
Transformations
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
Two Dimensional Viewing
3D Object Representation
• Object Boundaries: – Plane, – Curved Surfaces
• Object Interiors:
• Solid Objects:– Boundary Representation– Space-partition Representation
3D Object Representation
3D Transformation
• Transformation– translation, rotation, scaling
• Rotation in 3D– a composite of 3 rotations
• X-axis rotation
3D Transformation
3D Display
• View an object from any spatial position: front, top etc.
• Projection onto a flat viewing surface.
3D Display
Projection
• Specify a view plane
• Projections– Parallel– Perspective
• Projection transformation
• Clipping
Parallel Projection
Perspective Projection
Different Viewing Directions
Changing of Reference Point
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.
3D Surface Detection
Depth Cueing
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)
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.
Surface Illumination
Shading Techniques
Reflection and Transparency
Radiosity
Lighting Conditions
Colours in Computer Graphics
Colour Models
• Colour Model:– The method for explaining the properties or
behaviour of colour within some particular context.
• RGB Model: – based on tristimulus theory
Colour Models
Grey Scale
Logarithmic & Exponential
Colour Translation
Pseudo Colour Display
True Colour Display
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– Bull’s eye, cylindrical display
Slice-and-Dice
Ray Tracing
Surface Rendering
Volume Rendering
Bull’s Eye Mapping
Clinical Applications in Nuclear Medicine
• Hot Spot Imaging– Volume rendering with maximum activity projection
• Cardiac Imaging– Perfusion imaging(Bull’s 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.
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