Advance SHADING--BRDF

In fact, the bidirectional reflection (reflect) distribution function (BRDF) is a four-dollar function that ultimately calculates a ratio that determines how much of the light that is injected into the surface of the object is reflected by the surface of the object and is eventually seen by the eye. The more reflection, the more light the eye receives, the greater the brightness. So, the intrinsic type of this function is an adjustment function. The light source described here is Non-area light source. The physical expression of BRDF is

where L is the direction of the incident light, V is the direction of the light intensity we calculate, they are the unit vectors, it describes a microscopic phenomenon, regardless of the distance caused by the attenuation. The above-mentioned BRDF is a four-tuple function, which translates V and l into a spherical coordinate system and requires two parameters to represent each. El in the above refers to the irradiance of the incident light, which is the luminous flux on the unit area, while the molecule is the radiance of the reflected light. Why is the equation multiplied by an El to ultimately calculate the radiance instead of the reverse form? Because the radiance does not change with distance, this ignores the effect of the camera relative to the surface position of the object. Because as for why these two ratios are not radiance than the radiance? This is related to the measurement of BRDF.

In the actual use of the process, in order to get the most realistic simulation, the material will be simulated in advance BRDF data collection, so that in the rendering process directly using the BRDF data can be. If BRDF use the ratio of radiance and radiance, then to collect the incident light radiance, and radiance acquisition is very difficult, specifically not discussed here. However, it is convenient to collect the incident ray Irradiance, so the above formula is used to represent the final result.

In the Non-area light source, you can use a description.

Take it into the shading equation, it is the form.

Where el can be used in the "Advance shading--light Source Type" in the calculation formula to calculate, at this time elk is already after the distance attenuation value, also confirmed that BRDF described is microscopic phenomenon. (not to be continued)

　　

　　

　　

Advance SHADING--BRDF