Last Updated April 15, 2010

Lighting

  1. What is Lamberts cosine Law? How is it used?
  2. Compare and contrast Gouraud & Phong shading.
  3. Distinguish between diffuse and specular reflection of light. Provide a simple mathematical model for simulating the effect of diffuse reflection, and provide a model to simulate specular reflection.
  4. Compare and contrast the  Phong Specular reflection and Blinn-Phong Specular reflection models.
  5. Give examples from the real world of surface materials that are primarily diffuse and/or primarily specular.
  6. Why are surface normals important in lighting calculations?
  7. The image below shows 3 stacked spheres on a plane. There is one point light source in the scene. Three areas of the scene are labeled A, B & C. Describe each area in terms of the relative amounts of ambient, diffuse and specular light reflected.
  8. Examine the image above and give two reasons why the ground plane gets darker as you move from the bottom of the image to the top of the image.     
  9. Give a brief description of the following:-
    1. Diffuse Reflection of ambient light                                                 
    2. Diffuse Reflection of a point source of light                                   
    3. Specular Reflection                                                                          
  10. Given The following:- a point P on a surface, a unit vector n (normal the surface at point P) and  a unit vector s (vector to a light source). Derive an equation for the unit vector r (representing the direction of specular reflection at P) based on n and s.                                                            
  11. Compare and contrast Gouraud and Phong Shading. Give an example of the use of each of these shading models when a particular polygon mesh is being scan-converted.                                        
  12. Lambert’s Law and Phong reflection can model the way light reflects from a surface. Describe how these models work and their contribution to the reflected light.                                   
  13. How can specular reflection be computed without having to calculate the reflection vector?
  14. Explain in detail how OpenGL renders smooth shading and why it usually renders specular reflection poorly. Describe a technique to improve how specular reflection is rendered in OpenGL.
  15. In the scene diagrammed below, the light source is initially at “Position A”. The light source is moved to “position B”. Describe if the ambient, diffuse and specular reflections at “Point P” change due to the movement of the light. How do they change? Re-draw the  diagram, labelling all the important vectors and angles for lighting calculations.
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  16. Give examples from the real world of light sources best approximated by OpenGL point light sources, by directional light sources, and by spot light sources.
  17. A surface in OpenGL is given diffuse reflection coefficient of (0.8, 0.4, 0) and there is no ambient light in the scene.
    1. If a blue light is used what is the colour of the object and why? (2 marks)
    2. If a magenta light is used what is the colour of the object and why?
  18. Examine the two images below. The top image shows a 4x4 tiled plane with lighting showing specular reflection as the oval bright area. The bottom picture shows an attempt to reproduce this Scene in OpenGL with the light in the same position. Why is the specular area so much bigger in the OpenGL version? Why does the specular reflection have a hexagonal shape.

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