Concept of Computer Graphics

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Concept of Computer Graphics

  1. 1. 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
  2. 2. 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
  3. 3. Graphic Software • General Programming Package (Graphic Library in C etc) • Application Package (For None- programmer) • Modelling Transformation=>World Coordinates=>Normalised Coordinates
  4. 4. 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.
  5. 5. User Graphic Interface
  6. 6. Output Attributes
  7. 7. Transformation Pipeline
  8. 8. Display Processor in Graphic System
  9. 9. From Object Model to Display Device
  10. 10. Object Rendering
  11. 11. Basic Building Blocks For Pictures • Output Primitives – Characters, – Geometric Entities. – Lines, – Filled Areas, – Colours – Polygons
  12. 12. Output Primitives - Lines and Points
  13. 13. Output Primitives - Circles
  14. 14. Output Primitives - Polygon
  15. 15. Properties of the Output Primitives • How it is displayed: – Intensity – Colour – Style – Pattern
  16. 16. Geometric Transformation • Change size, position or orientation: – translation – rotation – scaling • Altering or Manipulating Display
  17. 17. Transformations
  18. 18. Transformations
  19. 19. 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
  20. 20. Two Dimensional Viewing
  21. 21. 3D Object Representation • Object Boundaries: – Plane, – Curved Surfaces • Object Interiors: • Solid Objects: – Boundary Representation – Space-partition Representation
  22. 22. 3D Object Representation
  23. 23. 3D Transformation • Transformation – translation, rotation, scaling • Rotation in 3D – a composite of 3 rotations • X-axis rotation
  24. 24. 3D Transformation
  25. 25. 3D Display • View an object from any spatial position: front, top etc. • Projection onto a flat viewing surface.
  26. 26. 3D Display
  27. 27. Projection • Specify a view plane • Projections – Parallel – Perspective • Projection transformation • Clipping
  28. 28. Parallel Projection
  29. 29. Perspective Projection
  30. 30. Different Viewing Directions
  31. 31. Changing of Reference Point
  32. 32. 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.
  33. 33. 3D Surface Detection
  34. 34. Depth Cueing
  35. 35. 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)
  36. 36. 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.
  37. 37. Surface Illumination
  38. 38. Shading Techniques
  39. 39. Reflection and Transparency
  40. 40. Radiosity
  41. 41. Lighting Conditions
  42. 42. Colours in Computer Graphics
  43. 43. Colour Models • Colour Model: – The method for explaining the properties or behaviour of colour within some particular context. • RGB Model: – based on tristimulus theory
  44. 44. Colour Models
  45. 45. Grey Scale
  46. 46. Logarithmic & Exponential
  47. 47. Colour Translation
  48. 48. Pseudo Colour Display
  49. 49. True Colour Display
  50. 50. 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
  51. 51. Slice-and-Dice
  52. 52. Ray Tracing
  53. 53. Surface Rendering
  54. 54. Volume Rendering
  55. 55. Bull’s Eye Mapping
  56. 56. 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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