Fast and Dirty Approximations

Rough Approximations:

• Use red, green, and blue instead of full spectrum
  • Roughly follows the eye's sensitivity
  • Forego such complex surface behavior as metals
• Use finite number of point light sources instead of full hemisphere
  • Integration changes to summation
  • Forego such effects as soft shadows and color bleeding
• BRDF behaves independently on each color
  • Treat red, green, and blue as three separate computations
  • Forego such effects as iridescence and refraction
• BRDF split into three approximate effects
  • Ambient: constant, nondirectional, background light
  • Diffuse: light reflected uniformly in all directions
  • Specular: light of higher intensity in mirror-reflection direction
• Energy flux L replaced by simple ``intensity'' I
  • No pretense of being physically true

Approximate Intensity Equation:

(single light source)

• stands for each of red, green, blue
• is the intensity of the light source (modified for distance)
• accounts for the projected cross-sectional area of the incoming light
• the k are between 0 and 1 and represent absorbtion factors
• accounts for any highlight effects that depend on the incoming direction
  • use if there is nothing special
• is the mirror reflection angle for the light
  • the angle between the view direction and the mirror reflection direction
• accounts for highlights in the mirror reflection direction
• the superscripts e, a, d, s stand for emitted, ambient, diffuse, specular respectively
• sum over each light l if there are more one