Lighting Design and Simulation Knowledgebase
(Term of computer graphics)
A stochastic process in which values are sampled uniformly over a rectilinear subspace. The exact position of the respective sample in each subrectangle is thereby varied randomly.
In the Radiance software, this method can be applied in several situations of the simulation process:
On the image plane, view rays may be sent through random locations within the area of a pixel instead of through its center. This feature should be applied together with image filtering, and helps to eliminate aliasing effects ("staircases") in diagonal edges of the image. Without filtering, pixel jittering may result in a slightly rough appearance of such edges.
Specular hightlights can be sampled with rays that deviate from the exact mirror direction of a surface to a degree controlled by the roughness attribute of the material. This feature results in correctly displayed highlights on materials that exhibit a high specular reflection component, but not such a smooth surface as to visually mirror their environment. If no filtering is applied to the final image, the boundary areas of specular highlights may show some speckle.
In shadow testing for a point in the scene towards a light source, rays can be aimed at random points on the source surface. This will result in soft penumbras, given that the image is filtered to a lower resolution after rendering. If the image is not reduced, then the stochastic sampling of light sources may result in speckle in the penumbra.
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aliasing image filtering penumbras Radiance software |
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| jittered sampling | (not translated) |
