“Timewarp” Artifacts – How to smooth out??

[Tim Wilson]

Hmmm, could be an excellent idea for a tutorial. Filters like this aren’t always as easy as they look.

In general, you’re going to want to start with Pixel Motion. The foundation of a technology called Optical Flow, it analyzes the position of pixels in each frame, and creates in-between frames by predicting where new pixels should be placed to create new frames.

It sounds like this is what you’ve done, because you describe some unpleasant surprises with interpolation.

A first step might be to raise the number of iterations, which will also increase the render time, of course.

You might also want to increase the number of motion vectors — that is, the number of elements being tracked to create the new frames.

The other thing to note is that if there’s a whole bunch of motion between frames, and the pixels move different amounts along different axes, it’s harder to predict where each pixel should be.

I once did an optical flow retiming with surfing footage from the ArtBeats library, and it looked fantastic…until the very end, where the wave wrapped in on itself. There was no way for the algorigthm to guess that the pixels had to move in a tight spiral between frames, so it calculated the distance between the pixels linearly, and looked more like a morph than a retiming. Way cool, but not what I was looking for. My solution there was to edit off those last frames and say “See how great it looks!”, but it sounds like you’re having problems in the middle of things.

So as you begin, try using simpler, slower footage to see more success as you begin to experiment. I know the temptation is to begin with dramatic sports footage or something, but your first steps will be firmer with less dynamic footage.

One thing to keep in mind is that AE’s implementation of this technology allows you to specify input channels. The green channel offers the clearest edges, so start there.

Also keep in mind that some footage is going to need more control than even this powerful new filter offers. Those super-duper specialized tools are what third parties are for. Check the Adobe website for third-party timewarp filters — they’re all darn near amazing, and they offer masks to isolate the areas of the frame (not just channels) you’re interested in, and other tools that you may find useful.

Last but not least, keep in mind that many of the shots you see that *appear* to be using this and similar effects are accomplished by overcranking the film or video (Thanks, Varicam!) frame rates. If you have more frames, you don’t need to interpolate — just change the rate. Massive control, teensy-weensy render times.

Without seeing the footage and knowing what you’ve done with each of the parameters, it’s hard to offer more than these few admittedly minor suggestions. If none of these work, pass along some more details and let’s see what we can figure out.

Tim

[Jack Binks]

Some great tips from Tim there. As well as raising motion vector detail (should there be lots of differential motion in the scene), the next port of call is to look at providing a matte layer. This helps minimise artefacts seen in areas of obscuration (i.e. where a foreground object crosses a background), so if you have such motion in your scene try creating a white solid and loosely rotoing it to follow the shape of the foreground region. Precomp this solid, staying in the current composition, apply timewarp to your source layer, then from the matte layer drop down pick the precomped white solid you just rotoed (if necessary, dependant on the matte you’re using you may need to change the channel picked under ‘matte channel’). Try flicking back and forth between a snapshot frame with the matte layer off, and the current frame with the matte layer specified…. does this clean up any artefacts?

As Timewarp is a based on a licensed version of our Kronos tech you may well find some useful information plus tips and tricks in the After Effects Furnace manual that can be found on our site….. check out http://www.thefoundry.co.uk Downloads->For After Effects->Furnace then click on the user guide link and look at the Kronos section.

HTH!
Jack

The Foundry, UK

[Joey Morelli]

Hey guys…thanks for the detailed input. I have been banging on this one clip for days – no luck. I have experimented with every parameter suggested and in the “Furnace” manual except for matte suggestions. I don’t want to get into all that…too much work. I didn’t expect that this new After Effects technology would take so much tweaking for a simple 50% speed reduction. It doesn’t measure up to the hype, IMHO.

I wish I could post a JPEG to show you what I am up against…but I don’t know how on the cow. It’s a surfer shot with the camera slpashing in & out of ocean water. I think I found out that Pixel Motion does NOT work well with water ftg…so I am screwed.

Anyway, thank you guys for your time.

– Joey

[Tim Wilson]

Remember the example I gave of surf footage that showed the limitations for working with water? This is what I was talking about. This is why surfing footage is an excellent example of footage that works best overcranked in the camera. Some effects can’t be created any other way.

As a result, the amazing Pixel Motion mode of Timewarp is simply the wrong tool for a straight time remap like 50%. Better to use frame blending. You may even get good results from one of AE’s older time filters. Heck, any NLE will do a decent job reducing the speed of a clip by 50%, and many will do it in real time.

So if you need a 50% speed change, use the right tool. If you want to use the Timewarp filter for the purpose of experimentation, use footage that’s better suited to it. Actually, nearly anything *but* water will work fine out of the box.

If you want to use the filter with the footage you have, in order to solve a particular problem, then John’s suggestions will get you there.

As always, match the tools to the task. You can sort of drive a nail with your shoe, but you can’t tie your shoes with a hammer at all.

In other words, some problems take more than a few clicks to solve, even with the right tools. Knowing which is which is why they pay you the big money.

And of course we’re happy to help here.

tw

[Joey Morelli]

“…If you want to use the filter with the footage you have, in order to solve a particular problem, then John’s suggestions will get you there. ”

Thanx, Tim… but Who’s John?

You are correct…definitely found the one limitation to “Pixel Motion”…water / surfing ftg. Water rolling over itself just doesn’t blend pixels well. Just so happens the DVD Motion Menus I am working have Hawaiian Surf ftg in them 🙁 I am stuck using frame blending (which softens the ftg a bit).

Oh well… thanx for your time, guys – much appreciated as usual 🙂

– Joey

[Tim Wilson]

[silversurfer] “Thanx, Tim… but Who’s John?”

Meant Jack from The Foundry (amazing plug-ins, buy them all).

Sorry about the boo-boo. Maybe Jack is one of those folks whose given name is John???

🙂

[Rafael Amador]

Hi Joey,
If you have the chance try Shake for any retiming.
salud,
rafael

[Joey Morelli]

Sory, man…don’t have $500 to blow on an app I will never use again for anything else. Thanx anyway for the suggestion.

– Joey

[Jim Dodson]

Jack–

I know this is an old thread, but I’m hoping you’re still subscribed…

I have a car pulling up to a house — no camera movement — and I am applying a 200% speed change.

As the car pulls up to the curb, the lawn in front of the house morphs and is affected by the car’s movement. So I did a very precise roto around the car and used that roto layer as a matte.

Unfortunately, the matte has no effect on reducing the artifacts… You had suggested a loose roto… Is my roto too tight? (It is precise to the car).

Thanks!

Jim Dodson

8 Core Intel — Mac – OSX

[Brian Horn]

I’m having similar problems with this. I’ve tried Twixtor and Timewarp and the equivalent effect in Apple’s Motion, all with less-than-stellar results.

From what I’ve seen, it depends almost ENTIRELY on the footage. I have a lot of ocean wave footage shot at 60fps 720p on a go-pro and it mostly looks good, but does result in those strange moments of water morphing that Tim mentioned.

I also have a shot for a short film I’m doing that is a wide of a couple tumbleweeds being thrown over the hood of a car. They cross over some power lines in the shot and the shot was intended to be a sort of “Zack Snyder” slo-mo nod. All these crisscrossing lines and fine detail of the tumbleweed branches drive Pixel Motion insane and the whole thing morphs from beginning to end. Not to mention the crazy aliasing of the power lines I’m getting from this 720p footage.

I’ve tried matting, adjusting parameters (in all three programs) and still nothing looks right.

Here’s the shot:
https://www.vimeo.com/28831317

I didn’t make this next video, but it’s supposed to be an example of how “awesome” this pixel motion stuff is. Check out the bike tire treads at :30, :40, and :45. Same warping going on.
https://vimeo.com/17905045

If Optical Flow’s effectiveness really does depend on the subject of the footage, doesn’t that make it entirely unreliable when you have to plan out a shoot?

-Brian
http://www.bullbythehorns.net

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