![]() The halfway vector approach avoidsĮxplicit computation of R, and is simple to implement. When it deviates from N, the angle of deviation is easilyįor simplicity, we replace W( q ) with a single constant k s. Now this vector is exactly equal to N if the vector V is parallel to Instead of measuring angles between N, L, V and R, we define a vector H as Specular Reflection - Halfway VectorĪ slight variation on the Phong model is the so-called halfway See the textbook for graphs of typical W( q ) values. While W( q ) is roughly constant over a large range of q values, it deviates at large q, especially as q approaches 90 o. Replaces the constant k d in the diffuse formulae. Small value will lead to a dull-looking surface. A large value (>10) will lead to quite a shiny surface. The quantity ns is called the Phong exponent and is used to control the The viewing direction, then the specular reflection due to a light source q is given by:įrom V to R. It is the vector pointing away from the surface such that R+L is parallel to N. ![]() L is, where L is the direction to the light source. Perfect reflector reflects light along a direction R which is at the same angle to N that Many surfaces exhibit a specular (shiny) reflection or highlight. The light source q, then the diffuse intensity due to the source is If N is a unit normal to the surface, and L is a unit direction to The more normal the source is to the surface, the (power/area) of the light hitting a surface from a source depends on the angle between the Mean their reflected light is independent of the source direction however. Most surfaces scatter light uniformly in all directions, no matter Directional Diffuse Reflection - Lambertian Surfaces Normally 3 values used for k d to take this into account. Note: Although the value k d is a scalar,Īll the lighting equations can be repeated once each for R, G and B channels. The amount of ambient light that reflects off a surface isĭetermined by the surfaces ambient-diffuse reflection coefficient, k d. We measure the intensity of ambient light with The simplest lighting model is a uniform field of light in allĭirections, which is called ambient light.
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