Light Shading

[ LiB ]

Light Shading

The observer looks at the scene and renders the scene based on its current orientation and position. If the observer is looking at a dog, the dog is rendered to the 2D image. To render the scene, each point in every object that's visible to the observer must be shaded accordingly . When rendering realistic scenes, you must shade each point for every visible object correctly to create a desirable image. You have to look at each point on an object and compute its color correctly based on a series of parametersthis is known as light shading . To shade a surface in extreme detail, you must visualize each point as an infinitely small area. This is known as the per-unit projected area . See Figure 4.4.

Figure 4.4. The per-unit projected area is an infinitely small area for every point on a surface.

NOTE

TIP

Light shading is the most important part of simulating light in a model because it's responsible for the final rendered image.

You must compute the amount of energy that is incoming and outgoing on the per-unit projected area based on the timely rate and flow of energy. This is referred to as the flux . Normally, when energy interacts with each infinitely small point on the surface, you use something called the solid angle to determine how much of it reflects off the surface. Let's talk about the solid angle for a moment.

The Solid Angle

A solid angle is a three dimensional version of a normal angle. A normal angle measures the angle between two line segments. The solid angle is constructed by placing a unit sphere on a projected unit area. The solid angle is used in understanding the flow of photons to the intensity of the light source. It is the angle measurement of a ray and the reflected direction. It can be viewed as a very tiny area on a unit sphere that determines the direction of the ray. See Figure 4.5 for an illustration of the solid angle. The solid angle is dimensionless and is expressed in something called steradians . It could also be defined by a surface normal and two orthogonal vectors. You use the per-unit projected area in conjunction with the solid angle to determine which direction the ray will be reflected off the plane of a surface.

Figure 4.5. The solid angle measurement of a ray as well as the reflected direction.

The following sections define the terms used in this book to help you better understand light scattering and interaction.

[ LiB ]