Many articles are giving highlights to the word radiosity, where we can see applications for animation lighting and games. But what is radiosity?

Radiosity is an addition to render methods that increase the realism of images. Conventional methods of lighting are based on reflection of the ray light, first on objects and then on the eyes of the observer. The radiosity method follows the nature model, where the reflection of the ray light jump from an object to another and then on the eyes of the observer. To visualize the radiosity, imagine a room with 1 white wall, one red and one blue. If we turn on a white light in the roof of this room, we can see that the white floor receives some contributions of red light from red wall and blue light from blue wall.

In many scenes, mostly interiors, there are zones that are not directly illuminated by the light source. In these cases, the illumination is the product of the reflected light, one or more times, from reflectors surfaces. The method of radiosity has the goal of calculating the illumination and shading in which predominate reflectors surfaces.

Proposed in 1984 by Goral, Torrance & Greenberg, from Cornell University, on the article “Modeling the Interaction of Light Between Diffuse Surfaces”, the radiosity algorithm has origin in the fundamental methods of the energetic balance, used in the thermal engineering. Radiosity can be defined as being the energy for unit of time and area on each point of the objects on the scene, where the incident luminous energy in a surface is reflected with equal intensity in all directions. The quantity of reflected energy can be characterized by the product between incident energy, quantity and the constant of surface reflection that should be specified as parameter of the object.

The most interesting about radiosity, is that the human eye is very sensitive to it. Even if the radiosity isn’t present, your mind will realize it immediately and will consider your image not real. It is important to note that there is a high cost processing and not always it will be the best solution. We can soothe this cost applying some simulations methods through the use of different kinds of lights.

Several programs for 3D rendering, such as Lightflow, already comes with the option for rendering with radiosity adjusted as standard. Although these methods are considered very fast, they will not be fast enough for use in games (real-time rendering).

Radiosity for Real-Time Rendering ?

The current methods of radiosity are so efficient that extrapolate the needs of the human brain perception. The method used by most of 3D engines has a solution where, after the development of the scenes and positioning of fixed lights, a program is executed to calculate the total radiosity and stores the contributions on light maps (or radiosity maps). The result will be a variation of the illumination deposited in the object map. This method is very efficient, but it has some limitations when working with dynamic lights or distant objects.