Computer Graphics Part 6b (Shading)

  1. What is the difference between the shading and illumnination model?
    While the illumination model computes the color of sample points, the shading model is the process that colors the whole surfaces.
  2. List 3 shading models
    • Flat shading (lighting computation is done once per polygon) -> less compputation needed
    • Gouraud shading(once per vertex)
    • Phong shading (once per vertex) -> heavy computation needed
  3. Flat shading
    Image Upload 1
  4. What is the major problem with the flat shading model?
    • suffers from matchband effect
    • humans are very sensitive to sudden change of brightness
    • the artefact remains even if polygon number is increased
  5. Exaplin how the Gouraud shaing works...
    Image Upload 2
  6. how to compute vertex normals and their funciton
    Image Upload 3
  7. What is the major problem with Gouraud shading?
    Image Upload 4
  8. Describe the Gouraud Shading model in 3 steps!
    Image Upload 5
  9. Describe the Gouraud Shading model in 3 steps!
    Image Upload 6
  10. Name the major problem(s) with interpolation shading and the solutions...
    • 1. In some cases a polygon might have additional vertices between two corners that belong to neighboring polygons and f-up the average. (sol1; subdivide into triangles, problems does not occur, sol2; introduce 'ghost' vertex that shares that vertex' values)
    • 2. Inside/Outside problem (add small polygon strips along edges or test angle and threshold to defeat averaging)
Card Set
Computer Graphics Part 6b (Shading)
University of Edinburgh School of Informartics Copmuter Graphics (Level 10) Revision Cards created by Simon M.