Light Transport Notation

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Light Transport Notation

In your photon mapping application, you will be developing two types of light interaction functionsreflection and refraction. But as you learned from Chapter 3, reflection can be broken into two sub-categoriesdiffuse reflection and specular reflection.

Most of the time, your reflections will be diffusive. You need to differentiate between which surfaces are diffusive and which ones are specular. Remember, specular surfaces are bright shiny reflections that reflect light in one particular direction. A good example of a specular reflection is a mirror.

In your model, you need to develop some notation that tracks the path light takes for reflection given the light source and different surface types. Let's first define some abbreviations.

L = light

E = observer eyes

S = specular reflection

D = diffuse reflection

Take a look at Figure 4.6 and try to determine each course the light takes. The ray that is released from the light source is recorded either as L, E, S, or D every time it interacts with an object in the scene. However, it may be possible to track the path light takes in the opposite manner (the path can be recorded from the observer as the origin).

Figure 4.6. Light transport notation helps describe the path light takes for each ray.

In Example 1, you can say the path light travels is LSDD. In Example 2, you can say the path light takes is LSSD. In Example 3, you can say the path light takes is LDDS. It is very important to understand the flow of light between different surface types if you are going to correctly simulate it. Light transport notation may be used later on in this book to illustrate the path a pho-ton may take from one point to another.

NOTE

TIP

Light transport notation decreases the complexities when explaining the path light takes as it intersects different types of surfaces in the scene.

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