[Figure 9.1] For a split-screen matte, half of the frame is matted out, and live action is shot outside the matte.

[Figure 9.2] The matte is reversed, and stop-motion animation is shot where the previous matte was.

[Figure 9.3] Both sides of the matted areas appear combined in the final composite.

Film Compositing
To better understand how visual effects are done today, it helps to understand a little bit about how they were done in the “old school,” before modern digital tools were available. For stop-motion, a good number of these effects came to fruition in the original King Kong, which brought together several different processes for marrying animation with live-action footage. One of the most basic compositing effects that can be done on film is a split-screen matte shot. It is so basic that I used it myself many years ago on my student film, Snot Living, at the University of Michigan, which I shot in 16mm. For a shot where my live actor, Brandon Moses, stared at the animated clay puppet in the same shot, I simply framed up my shot and attached a glass plate to the camera lens with poster putty. In the area where I wanted the puppet, I masked out that part of the frame with black paper on the glass, creating a matte (Figure 9.1). The black matted area would not be exposed on the film, but the rest of the frame would. In the area surrounding the matte, I shot Brandon in live action. Next, I had to rewind the film to the same frame where I started, cover up the rest of the frame with black paper, and remove the previous matte, essentially reversing it (Figure 9.2). Then, in this area, I shot my animation through another pass on the same frames in the camera. After sending the film to the lab and getting it back, both exposed elements were blended together into the same frame (Figure 9.3). The risk in using this technique was that if something went wrong with either side of the matte, the whole shot would need to be re-done.

[Figure 9.4] Live action of the actor is shot with the space above his head matted out.

[Figure 9.5] The matte is reversed, and stop-motion animation is shot where the previous matte was.

[Figure 9.6] Both sides of the matted areas appear combined in the final composite.

I used the same technique for another shot in the film, where Brandon gets hit in the head and three tiny versions of the clay puppet spin around his head (like in those old cartoons where little birds or stars would spin around a character’s head after a serious injury). In this case, the matted area where the animation happened was a tiny rectangular space near the top of the frame (Figures 9.4 to 9.6).

The extra trick with this shot was that because most of the frame was matted out, I was able to rig a large set in the same place that Brandon had been lying earlier. Because I wanted the puppets to look like they were spinning in mid-air, I placed them on a horizontal sheet of Plexiglas so that the background would show through. The Plexiglas was held up (precariously) by two footstools and a stack of phonebooks on each side to bring it up to the level of the matte window. This whole set-up actually came crashing down in the middle of my animation, but luckily I was able to set it back up and place the puppets back where I thought they had been. Surprisingly, it worked, and I didn’t have to re-shoot anything, which was a complete fluke and stroke of dumb luck. (Snot Living can now be found on YouTube by typing the title in the Search window.)

The limitation to the split-screen matte is that the live-action and animated elements in each half of the shot cannot cross the matte line. If they do, they will be cut off. For this reason, the effect can only be used for certain shots where the two elements don’t need to cross over each other. For shots where a stop-motion puppet needs to move across a live-action frame or interact with it, Hollywood movies have used rear projection, a technique in which a puppet would be animated in front of a movie screen projecting previously shot live-action footage one frame at a time. The puppet would be moved to match the background, the camera took a frame, the rear projector advanced to the next frame, and the process repeated. For any moments of interaction, the puppet was simply positioned to match up to the live-action footage behind it. This was the basic premise of Ray Harryhausen’s Dynamation process, which would also be combined with matting out any foreground elements in front of the puppet, and matting them back in through another camera pass. When you understand how they did this, it makes watching those old Harryhausen films that much more awesome.