Incitatus
11-07-2003, 07:34 PM
I thought I'd write this down because I've noticed some of the newer members drowning in all the terms and expressions one might come across when reading about rendering and in particular advanced renderers like Vray and Brazil.
Pls feel free to add anything or more importantly correct any mistakes :)
Raytracing -
Very simply raytracing is tracing the path of a lightbeam in a scene as it bounces around. No scattering or 'GI' involved :)
GI, Global Illumination -
First of all what Gi is not. GI is not rendering an image with light coming from all directions around the object, or a globe around the object. Global Illumination is the principal that when light from a source hits a surface it is reflected and scattered around. If the surface is perfectly diffuse it reflects the light in all directions making a globe shape if you will :). In the real world of course light hits a surface scatters and reflects millions of times. A renderer can only scatter the light a little bit and follow it for a couple bounces, but doing so it can calculate a pretty good looking global illumination. These are those realistic looking renders with the soft shadows :).
Radiosity -
The most popular ways of calcutalting GI are radiosity and Monte Carlo (see below). Radiosity calculates the energy projected by the source on to the object and stores the info on the actual surface. So to get a smooth result radiosity needs to tesselate the scene to store the lighting info. Which is why you need to adhere to certain rules when modeling if you want to use radiosity.
Monte Carlo -
Monte Carlo is a raytracing technique that stores the lighting info apart from the rest of the scene. AS far as I understand it, it sends out random rays from the objects (unlike radiosity which tarts from the lightsource) in the scene, follows there paths and scatters them for a certain amount of bounces, then discards the rays it doesn't need. This is used by most advanced renderers.
HDRI -
High dynamic range images. A regular bitmap contains pixels that can range in brightness from 0 to 255. HDR images can contain far greater contrasts e.g. 0 to 20.000 and therefore are a far more realistic. When projected on a sphere around a scene and used for lighting they produce an extremely realistic effect. An added feature is the ability to change the exposure time as you would when using a camera.
DOF -
Depth of field. The same effect as when using a camera. a lense can only have one focal distance, the distance at which everything appears perfectly sharp. Points in space within the focal distance get projected before the film and points futher than the focal distance beyond the film. This meanes blurriness :). DOF in 3D is simply away of copying this real world effect. The amount of DOF depends n the size of the lense and the size of the apperture.
[EDIT] LOL This was more work than I thought it would be. I'll try to correct and add more stuff later. :D
Pls feel free to add anything or more importantly correct any mistakes :)
Raytracing -
Very simply raytracing is tracing the path of a lightbeam in a scene as it bounces around. No scattering or 'GI' involved :)
GI, Global Illumination -
First of all what Gi is not. GI is not rendering an image with light coming from all directions around the object, or a globe around the object. Global Illumination is the principal that when light from a source hits a surface it is reflected and scattered around. If the surface is perfectly diffuse it reflects the light in all directions making a globe shape if you will :). In the real world of course light hits a surface scatters and reflects millions of times. A renderer can only scatter the light a little bit and follow it for a couple bounces, but doing so it can calculate a pretty good looking global illumination. These are those realistic looking renders with the soft shadows :).
Radiosity -
The most popular ways of calcutalting GI are radiosity and Monte Carlo (see below). Radiosity calculates the energy projected by the source on to the object and stores the info on the actual surface. So to get a smooth result radiosity needs to tesselate the scene to store the lighting info. Which is why you need to adhere to certain rules when modeling if you want to use radiosity.
Monte Carlo -
Monte Carlo is a raytracing technique that stores the lighting info apart from the rest of the scene. AS far as I understand it, it sends out random rays from the objects (unlike radiosity which tarts from the lightsource) in the scene, follows there paths and scatters them for a certain amount of bounces, then discards the rays it doesn't need. This is used by most advanced renderers.
HDRI -
High dynamic range images. A regular bitmap contains pixels that can range in brightness from 0 to 255. HDR images can contain far greater contrasts e.g. 0 to 20.000 and therefore are a far more realistic. When projected on a sphere around a scene and used for lighting they produce an extremely realistic effect. An added feature is the ability to change the exposure time as you would when using a camera.
DOF -
Depth of field. The same effect as when using a camera. a lense can only have one focal distance, the distance at which everything appears perfectly sharp. Points in space within the focal distance get projected before the film and points futher than the focal distance beyond the film. This meanes blurriness :). DOF in 3D is simply away of copying this real world effect. The amount of DOF depends n the size of the lense and the size of the apperture.
[EDIT] LOL This was more work than I thought it would be. I'll try to correct and add more stuff later. :D