Traditionally, to render is to purify animal fats. For that topic, see rendering.
In computer graphics, rendering is the process of drawing a bitmap image based upon more abstract image information, such as vector graphics or 3D computer graphics information (typically consiting of geometry, viewpoint, texture and lighting information).
In the case of 3D graphics, rendering is a slow, computationally intensive process (typically for movie creation) or supported by realtime 3D hardware accelerators in graphic cards (typically for 3D computer games). The term is by analogy with an "artist's rendering" of a scene.
When the pre-image (a wireframe sketch usually) is complete, rendering is used, which adds in textures, lights, bump mapping, and relative position to other objects. The result is a completed image the consumer or intended viewer sees.
For movie animations, several images (frames) must be rendered, and stitched together in a program capable of making an animation of this sort. Most 3-D image editing programs can do this.
There are a number of different phenomena that need to be simulated when rendering a scene:
- diffuse reflection
- specular reflection
- global illumination
- depth of field
- motion blur
All 3-D rendering software and hardware produces an approximation to a solution of the idealised rendering equation. Slow movie-creation software typically use more realistic rendering equations than realtime 3D hardware accelerators.
Methods of rendering include:
- the painter's algorithm
- Ray tracing
- Global illumination
- Scanline algorithms
- Z-buffer algorithms
The current state of the art in 3-D image description for movie creation is the RenderMan scene description language designed at Pixar. (compare with simpler 3D fileformats such as VRML or APIs such as OpenGL and DirectX tailored for 3D hardware accelerators).
Movie type rendering software includes: