filtering light grain / denoise *before* resize?

[phædrus]

I'm going to encode an older British TV miniseries from a DVD -- it appears to be sourced from 16mm film. I'm not concerned about preserving the last bit of sharpness and detail, because it isn't especially sharp to start with. I would call the film slightly grainy. I'm using DivX and I may need to keep the bitrate down to about 1800-1900kbps to keep it to 1 CD per episode.

Mostly I have been doing backups of modern TV shows, so I don't have much experience with older, grainier material, even though the grain in this film is pretty mild. Obviously I'd like to remove most of the grain, so as to spend the bits better on actual elements of the scene instead of noise.

What would you suggest as the most efficient filters for light grain? I'm using an AviSynth script with VirtualDub 1.5.10.1 -- so it would have to be a filter that will work in that context.

Over on the AviSynth forum discussion on smoothing and sharpening filters, some say that dealing with film grain is different from dealing with other noise. I guess using Undot is a no-brainer. Plus what? FluxSmooth? TemporalSoften? What if I used all three? I'd appreciate expert opinions.

Also, I have a question about the order -- what about de-graining prior to resizing? This would be slower, but does it offer any advantages? It seems to me intuitively that it might. Gordian Knot puts Undot and denoising filters AFTER resizing when it writes an AviSynth script. But I wonder if that is really optimal in terms of picture quality. Wouldn't resizing tend to smear out the grain among adjacent pixels and make denoising a little less efficient? It seems to me as if it might. (I usually resize full screen material like this to 452x640, FWIW.) Since I don't really understand how these filters work, maybe I'm worrying over nothing here, but I thought it wouldn't hurt to ask.

[hakko504]

I'd try moving undot only to a position before the resize, and select the smooth resizer.

IIRC the major advantage of having filters after resize is that you gain speed, in your case probably ~40% (of the filter speed) by having the filters after resize. Depending on your computer you may consider this as a serious problem or not. But it also depends on what you're trying to do. Smoothing effects will be more noticeable if they are applied after the resize, while sharpening effects can be annihilated by the resize if you choose a bad resizer.

In short: There is no way of telling whats best unless you actually try it out. Cut out a short but (quality wise) bad part of the movie. Encode it with a couple of different filters/filter orders and then play it back a few times and choose the combination that gives you the best result.