Originally Posted by chirpie
All great points, (And I love how Steven is always shooting George down. ^_^) but it is true that SOME CG has added noise to better composite it into shots due to limitations of the source CG. Just not in the case of these particular movies.
Noise is also added to CG as a popular trick to help mask gradients and banding as a result. Some CG has it for stylistic purposes, others really do need it to cover up the limitations. Steven might be able to afford it, but it's a broad stroke saying "no limit due to CGI" for everyone. It really depends on the situation.
Visual effects for film are usually done to what is sometimes referred to as full negative density: ie the final result matches the dynamic range on the original scanned camera negative.
There is usually a "look" grade supplied by the productions color grader: this helps as a check to ensure that when the negative is graded the CGI is robust enough to stand up to the sort of grading that a normal camera neg would go through. In particularly CGI heavy scenes the shots will usually be given a normalised grade for consistency throughout the scene: this is to avoid having to drastically rejig the lighting on the CGI on a per shot basis .
However most VFX shots would be delivered without any overall grading beyond color matching of elements incorporated into the final image. They will match the original scan in overall color , range and grain.
Grain is applied to cgi in order to match the plate its composited into or if its an entirely CGI shot to ensure it matches the grain structure of the other shots in a scene next to it.
It is not normally necessary to apply grain ( or even crude noise) to professionally created CGI to mask quantisation errors. Even if you work with video most people will generate CGI at a higher dit depth and dynamic range than the surounding footage to aid integration.
Grain is not thrown over CGI willy nilly it is applied carefully to visually match the negative as scanned, as required.
Visual effects shots with mismatched grain do not get approved in professional film work.
At the DI additional grain management will be undertaken to produce the desired final look for the director: essentially replicating any old lab techniques that are desired: bleach bypass for example although some people prefer the real chemical process especially in this case. Grain management also gets applied to even out differences in stock over a scene .