Light Fields are another flavour of Image Based Rendering. Light Fields simplify the 6D BRDF by dropping the light direction dependency. With a well parameterised Light Field it is possible to generate new images from an arbitrary view point. Nevertheless due to the simplification it is not possible to re illuminate the scene or surface.

A new image from a light field can be easily generated by searching in the ray space (slab) for a similar  ray to the desired one. Several parameterizations for the slab can be chosen to allow the “indexing” and “query” of the light field. [1] ,[2] and [4] present a two plane parameterization to sample the light field, while [3] presents a spherical parameterization.

The two planes, one containing the camera sampling positions (s,t) the other contain the the image plane (u,v), are parallel aligned along an axis. A ray r(s,t,u,v) is fully describe by the intersection points in the planes (s,t) and (u,v).   The lumigraph [4] requires additionally the depth for each sampled r(s,t,u,v) two preform a depth correction in the final rendering stage, while [2] requires the transformation matrix for each camera position two allow a dynamic reparameterization and to explore other photographic effects such as variable focus and depth of field.

The rendering is divided into two stages: (i) query the slab for the most similar rays; (ii) combine the resulting rays to approximate the desired ray. The nearest neighbour is the most simple and easy to understand and the pseudo code is

    forall pixels in the image

        shoot a ray from camera position towards (st) and (uv) planes

        compute the interception points (s’,u’) and (u’,v’)

        obtain the closes ray to r(s’,t’,u’,v’)

        render pixel

The resulting image will contain a significant amount of undesirable artefacts. To reduced the amount of artefacts [1] suggests the use of bilinear filters in both (s,t) and (u,v) planes, while [4] uses the depth information to perform part of the filtering.

A more comprehensive survey in Image Based Rendering and Light Fields can be found in [5].