I am sitting here in my new favorite café/restaurant in Berlin, the Rebellion des Zimtsterns¹ and wait for the dish of the day. I really need a break from the inconvenient truth I have learned a few minutes ago. If you read on there’s also a short tutorial on a possible wire removal workflow. Skip it, if you already know it.

EDIT: Of course I couldn’t finish this lengthy post in one lunch break so I posted it the next morning.

As some of you already know I am working as an intern at rise visual effects here in Berlin and spend my days working with Nuke, Combustion as well as Avid, the latter two being a major pain in my brains. Rise is currently doing the VFX for quite a number of international projects, putting me in the position to participate on some of them with minor shots. I keyed and comped² for the German TV movie Die Patin some dull green screen shots, helped out with a replacement of an Oslo tram sign for the Norwegian movie Appelsinpiken as well as designed a fake UI for a screen replacement in the same movie. And after messing around with Avid on the company’s demo reel for two and a half weeks I was assigned to one shot for the upcoming Warner Bros movie Ninja Assassin.

The shot is equivalent to the movie’s title: Two fighters, one ninja and the protagonist (probably Rain, but it is hard to tell because of all the action going on) stand on wet asphalt in the middle of a street, their blades crossed. A car sends both of them flying into the air, Rain lands in front of the camera on a dark stunt patch whose fabric matches the tarmac not really perfect. And both stunt men are rigged with fat wires for their stunt, the camera panning along.

This shot from scene 98 is 136 frames long and one hell of a wire removal. Everything is moving and shifting, the overall lightness changes all the time depending on the headlights of the other cars and the wires move wildly behind and in front of the flying men. Seen from the compositor’s point of view: Hell. At least close to it.

On Friday I really started out with Combustion and felt quite lost at first. My co-worker Sascha introduced me to the Painting tool and I started painting like crazy and was certain to have that shot finished by Wednesday. On Monday I looked at it again and it just was awful. Jittering, double images, offsets and all the things you don’t want to see when you expect to see the background instead of the wire.

I couldn’t find a quick tutorial or at least a guideline on the web on how to start out with that kind of shots so I learned by trial and error. For any of you interested in a short guideline on how to pull of wire removals here’s what I suggest, thanks to Florian, Sascha and Jonathan for helping me find my way through to this. Hence I am not allowed to post any stills from the shot I will deal here only with basic concepts.

How to remove the wires

The Topmost Layer – Foreground

Take out your scissors, it’s roto time! The first step is nearly always to rotoscope the wires tightly but not too tight, you want to add about 3 or 5 pixels surplus on each side, in case you need to feather your mask later on. And probably you will. Pay special attention to the parts where the wire disappears behind the actors and make this really perfect that you won’t have to deal with partial removals in that areas later on.

The Bottommost Layer – Solids

If your shot is like mine and provides you with a couple of frames where the wires are shot against a (more or less) uniform solid (such as the sky) you can put a layer with the original footage below the layer with the cut out wires and. Now nudge the original so that the solid color will look through where the holes of your wires are. It is advisable to do this for each wire separately so you don’t have to make any compromises. Also don’t compromise with the areas where you have background features because we will make a clean plate of those parts.

In the Middle – Clean Plates

For any background that has features you will need to draw a clean plate from your original material now. That means to use the clone stamp (or it’s equivalent, depending on your tool of choice) and to paint out any of the actors and wires for one frame. Attention: This is no photograph where it doesn’t matter what portion of the background you use to paint out a wire! Hence it is an animation you have to paint exactly the obscured background. You do this by setting your clone source to a frame later or earlier in your sequence when the part you want to paint over is not covered by any foreground elements. If the actors are moving quite a lot it should be done in no time, but usually you have to use half a dozen or more source frames to clone one. If the actors are very static and there is no way to get a clean view on the background behind them you have to fabricate some background yourself. Make sure it is always your background that’s showing then, otherwise the features will flicker.

Place this clean background under your rotoed layer and on top of your sky-nudge-layers after you cut out the sky from your clear plate as well.

If the camera is moving too (like in my case) then track your background clean plate to the camera movement. The combustion tracker works really well but is not perfect. So you might want to nudge your plate in position yourself.

And here’s the tedious task: You need a clear plate of the background whenever it has changed. In my case the camera was moving wildly and it still was the same background after 100 frames, but from a slight different angle and very different lighting conditions.

The Colors Change!

I was not very lucky with my shot and the brightness and color values kept changing all the time so even my clean plate and nudged background did not always match the foreground. The only way I saw fit was to have an animated color correction in every layer but the original one. So I raised and lowered gamma values somewhere far beyond the decimal place frame by frame until it looked right.

That’s it?

In fact: No. Until now I was only writing about the background. But what about wires in front of your actors? In my case one of them has wrapped the wire even around his torso so he could be lifted even higher in the shot.

If your actors aren’t moving much but the wire is, you should be fine by painting it out frame by frame but be very careful and alert about any changes of lighting and motion and do it like the folks at Disney: After every paint stroke view it in motion with the frames before and after. In fact it is possible to pull it off in Photoshop (you will love CS3 Extended for importing image sequences and being able to use the healing brush in case you can’t use or don’t want to use one of Combustion’s greatest features: tracking paint strokes over time to certain features).

If there’s a lot of action going on any most of it will be lost in motion blur it becomes a little easier for you, the same way it becomes harder when there’s not much motion in the picture and a constant wire removal in the same place to do. The only way to pull this off I see is to make a small clean plate of the area in question and employ a four-corner pin or warping or that kind of stuff on top of it. It will be a lot of nudging and fine-tuning but in the end it will be much smoother than fidgety paint strokes.

Quality Assurance

Just as you think you’re done, it gets ugly: To ensure the quality of your work crank up brightness and contrast of your viewer and view our work whether it really matches the background and prepare yourself mentally to be busy for another couple of hours. Some masks won’t fit all too well, some colors are a little off and some things you expected to be in the blacks aren’t that black at all.

Phew, that was more than I expected…!

But you said something about a….

Yes, I mentioned learning about “an inconvenient truth” in the beginning, right?
As of one hour ago I was positive to be finished by Friday with the whole shot, already having done a great deal of the work. Only some minor painting and corner pinning would’ve been necessary. Shortly before taking my lunch break Florian, my supervisor asked me to look into the scene’s references folder. “There are only five frames in it” I replied puzzled. “That’s right! Those are the frames that will be in the current edit. So render what you got with additional four frames before and after and you’re done on this!”.

Five frames. The five frames of the car hitting the two guys. That’s a little more than a fifth of a second! I was hoping to be done with the shot by Friday, still I don’t feel satisfied with the shot anymore.

1. translates to The Rebellion of the Cinnamon Star [back]
2. I will keep this kind of short form of “composited” from now on, so better get used to it [back]