Computer Graphics Part 6b (Shading)

While the illumination model computes the color of sample points, the shading model is the process that colors the whole surfaces.

• 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

• suffers from matchband effect
• humans are very sensitive to sudden change of brightness
• the artefact remains even if polygon number is increased

• 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)