Contents  Introduction  The Rendering  Spectrum  Image-Based  Rendering  Lens Flare and  Bloom  Billboarding  Bibliography  Buy RTR from  Amazon.com  Printable version

6.1 The Rendering Spectrum

Up to this point in the book we have focused on showing three dimensional objects on the screen by representing them with polygons. This is not the only way to get an object to the screen, nor is it always the most appropriate one. The goal of rendering is to portray an object on the screen; how we attain that goal is our own decision. There is no correct way to render a scene. Each rendering method is an approximation to reality, at least if photo-realism is the goal.

Polygons have the advantage of representing the object in a reasonable fashion from any view. As the camera moves the representation of the object does not have to change. However, to improve quality we may wish to substitute a more highly detailed model as the viewer gets closer to the object. Alternately, we may wish to use a simplified form of the model if it is off in the distance. These are called level of detail techniques (section 7.3). Their main purpose is to make the scene faster to display.

However, other techniques can come into play as an object recedes from the viewer. Speed can be gained by using images instead of polygons to represent the object. It is less expensive to represent an object with a single image which can be quickly sent to the screen. Algorithms that use images to portray objects are a part of image-based rendering. One way to represent the continuum of rendering techniques is from Lengyel [8] and shown in figure 6.1

  

Figure 6.1: The rendering spectrum. (after Lengyel [8])

Within the field of real-time rendering, global illumination techniques such as radiosity and ray tracing are not feasible except on extremely high-end machines (or for simple demonstration programs). Such techniques will undoubtedly move into the realm of real-time as processor speeds increase. Currently these algorithms' main contribution to real-time rendering is in precomputing data such as vertex colors, light maps, environment maps, etc.

Next : Image-Based Rendering