3D Rendering Techniques

Radiosity is a global illumination algorithm used in 3D computer graphics rendering. Essentially, it realistically simulates the way light interacts in an environment. In the 1960’s engineers developed methods for simulating the radiative heat transfer between surfaces. Radiosity developed from this and it was introduced as a rendering method in 1984 by researchers at Cornell University. Radiosity helps to add an element of realism. An example is below.

In the left image, there is no radiosity. Lighting is present but it is simple. It looks like a blocky 3D model. In the right image there is radiosity. The shadows look softer and the light looks more real. It makes it more realistic looking than the other image. Radiosity does have limitations, though. It struggles with sudden changes in visibility, such as hard-edged shadows. Radiosity is also rarely used for specular and glossy reflections. So advantages of radiosity are, that it looks more realistic in every aspect, using shofter shadows, indirect lighting and colour bleeding. Also, 3ds max’s real-world lighting interface allows for the characteristics of real-world lighting fixtures to be defined. But radiosity also has disadvantages compared to standard lighting such as the render time. It is not advisable to put radiosity on a scene until you are ready for the final render, as everytime you want to look at it, it will take ages to load. 

Light intensity is specificed using photometric units. Examples of photometric units are lumens and candelas. The reason for there being multiple types of measurement units for photometric units is because of different types of light. A high luminous light is measured in lumens. A luminous flux concentrated into a narrow beam is measured in candelas. So the different measurement units are because of how light act, (its concentration, its wave length, reflections, etc.). Simply put photometric units are units used to measure quantities of light.

Local Illumination algorithms,(algorithms are a set of mathematical instructions for completing tasks) describe only how individual surfaces relect or transmit light. What this means is, using a description of light arriving at a surface, it predicts colour, intensity and distribution of light leavin the surface. So the algorithm calculates how light acts. If a surface should look shiny, it will calculate that it should and make it look shiny.

Global Illumination algorithms take into account how light is transfered between surfaces. Taking into account where the light comes from, and how it reflected, it makes the lighting look as realistic as possible. 3ds max has two examples of global illuminations; Ray-tracing and Radiosity.

Ray-tracing is also a ray-tracing is a global illumination based rendering method. When light rays hit an object, one of three things can happen; absorption, reflection and refraction. Ray-tracing mimics this. It traces rays of light from the eye back through the image plane into the scene.

This site has good examples of how ray-tracing works. http://www.siggraph.org/education/materials/HyperGraph/raytrace/rtrace1.htm

Ray-tracing and radiosity work together, and help cover each others disadvantages. Radiostiy is good with diffuse-to-diffuse inter-reflections. Its disadvantages are that its 3d mesh takes up memory and it doesn’t account for specular reflections. Ray-tracing is good with rendering specular reflections. Its disadvantages are that it takes long amounts of time and it doesn’t account for diffuse reflections.