【Real Time Rendering 5】
1、In radiometry, the function that is used to describe how a surface reflects light is called the bidirectional reflectance distribution function (BRDF).
As its name implies, it is a function that describes how light is reflected from a surface given two directions—the incoming light direction l and outgoing view direction v.
This illumination is measured at the surface as irradiance dE. The surface then reflects this light in various directions. In any given outgoing direction v, the radiance dLo is proportional to the irradiance dE.
The ratio between the two, which depends on l and v, is the BRDF.
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