Can GOP encoders detect noise?

[ExperimentalAnimations]

Given that the P frames contain the difference between the current and previous frames, can AVCHD detect between the identical non-moving pixels to be discarded and identical non-moving noise like fixed pattern noise, or even moving noise like grain?

[Ghitulescu]

The noise exists only in your brain, for computer everything is bits and bytes.

This is the problem with all denoisers, it's hard to distinguish the noise from eg film grain, snow, rain, sand, to name a few.

[Lyris]

Yes, it's all motion. Doesn't matter if it's unwanted videotape noise, wanted film grain, unwanted film grain, rain...
Some encoders have pre-filters for noise though.

[Ghitulescu]

Yes, it's true.

The only good way of removing true noise (not film grain) is to have several passes of the same material hoping that the noise would cancel itself. This is how is done in film/photo scanning, if one has time, and I've learned that some people do this for VHS, too. On the other hand, noise that is already in the original recording can only be removed using trial-and-error techniques :), since the PC cannot distinguish the noise from some details which may get lost in the process. The human operator is required to draw the line between noise and details.

[Lyris]

^ I did that for a film I had to master from an old Betacam SP cassette. It did result in some noise cancelation, meaning that I could use less aggressive temporal smoothing to remove videotape noise.