Cartoon mode is a set for two differnt things, both designed to help with cartoons:
- detect_static_motion is a motion estimation flag. The threshold below which a macroblock is concidered static is tripled, or something like that. It really helps saving many bits with would otherwise be used to code noise on a static picture.
The backgrouds should be at least as solid as with divx3.11 but I personally fear trails left by moving objects on smooth backgrounds (again, like old divx).
- vop_cartoon .. do you remember 'infamous' TOOSMALL_LIMIT? It's about quantization - when a block is motion-compensated well enough (with total error below the limit) it's just not coded at all. XviD doesn't drop any data in normal mode (limit = 1), but drops quite a lot in cartoon mode.
Again, this usually means that noise is ignored. It might also remove some small details, but small details shouldn't really happen in "proper" cartoons.
I would like to hear all your impressions about cartoon mode. You can even try it on normal movies and see what happenes. I expect a "nandub feel"