Maya Rendering Guides

Diffuse Reflectance

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Surfaces with diffuse reflectance scatter light equally in all directions. The amount of light reflected is directly proportional to the angle of incidence of the incoming beam of light. Diffuse reflectance can be observed on dull objects such

The exact math to calculate diffuse reflection was proposed by Lambert and so this reflectance is often referred to as Lambert reflectance. If we assume the light to have a diffuse color of (R^, Gz-j, Blcj) and the surface to have a diffuse reflection coefficient of (Rj, Gj, Bj). then the diffuse color component of the reflected light can be calculated as

(Rnl' Grti' Brd' " <RidRd*coste>< GjdGdcos(OK BidBdcosiei)

where 8 is the angle between the incident ray (direction of light source) and the normal to the surface at the point of incidence. So if 0 is 0 (the light hits the

Fig.6.11: 6 used in the diffuse reflection calculation

Surface

1. 6.11: 6 used in the diffuse reflection calculation surface straight on) then the diffuse reflection is the brightest, but light incident on the surface at more than 90 degrees (cos(>90) <= 0) causes no light to be reflected, and the corresponding area appears black. The diffuse color component of a light essentially models the color of the light as we perceive it.
2. 6.12: Spherical surface with diffuse reflectance

Let us apply ambient and diffuse reflectance to our famous snowman from Chapter 5. In Example6_3, we define all parts of Snowy to have the same ambient reflectance. The ambient color is slightly blue and is defined in the toplevel function, draw_Snowman as