"Cousin Ricky" <ric### [at] yahoocom> wrote:
> "clipka" <nomail@nomail> wrote:
> > Just of curiosity: Is there any benefit of the "big normals" approach at blurred
> > reflections over the "micronormals" approach?
>
> Pardon my ignorance, but what is the "big normals" approach?

To generate blurred reflections or refractions with standard POV, the most
common approach is to define *some* normal pertubation on the surface, and make
sure POV renders each pixel multiple times with differently pertubed normal,
averaging the results.

The "micronormals" approach uses a very fine-grained bump map for this purpose -
smaller than a pixel in size. Rendering such a scene with strong anti-aliasing
automatically causes POV to sample each pixel multple times and also take care
of the averaging, with the slight offsets in the ray resulting in different
pertubation.

The "big normals" approach instead uses very large-scale bump maps - e.g. larger
than the whole picture. Multiple sampling is achieved by rendering the shot
multiple times, while the variations in pertubation are generated by
translating the bump map by a (large) random offset. Averaging is done in a
post-processing step.

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