Video Editing: Superb Superimpositions (page 2)

Classic Hollywood technique pushed this concept to its limit in the montages that were once common in movies. A montage varies the shots in both images at once and sometimes adds a third stream or even more.

Here's a cliche example: Visual stream A shows successive shots of our heroine performing on the violin, plus audiences applauding, plus heroine bowing. Stream B shows mighty presses spewing out newspapers plus spinning front pages that stop in big closeup to reveal VIOLINIST CHARMS CROWD, and PRODIGY'S CONCERT SOLD OUT! Stream C presents recurring shots of trains roaring past or train wheels churning or station signs for different cities. Stream D shows concert posters and theater marquees, starting with PODUNK ELKS CLUB and escalating to CARNEGIE HALL, NEW YORK.

Whew! In about ten seconds, you've told the audience all they need to know about the rise of Helga Hergesheimer from unknown fiddler to world-class star. Though montages fell out of fashion some years ago, they may come back because multiple image streams are so easy to create in digital editing. Even if you have only two visual tracks on your editing timeline, you can combine and save two streams at a time, and then re-combine A+B, C+D, E+F, and so-forth, without losing image quality.

Superimposition is also the key to special effects using double exposure by means of A/B-roll editing. A/B-roll editing consists of using two separate video tapes, A and B, to edit together a single video. To tape a double exposure, lock the camera very firmly on a tripod and record the shot that will form the A roll of the action. Replace the tape with the B roll cassette being exquisitely careful not to bump the camera. Record the B roll shot. In editing, you align the A and B rolls and then transfer both at once with a video mixer, creating a superimposition.

Here are just a few of the many special effects you can create with double exposure:

• Teleportation: By dissolving from an empty scene on roll A to the same scene with an actor on roll B, you "beam down" the character into the scene. ("Beaming up," of course, uses exactly the opposite technique).
• Ghosting: If you leave the teleportation dissolve at 50/50, the background will seem solid while the actor appears transparent. If the actor lies quite still in shot A, then gets up and moves in shot B, the "ghost" will appear to leave the "body" behind. In this case, it would look more convincing to make shot A, with the body, 75 percent and the ghost in shot B 25 percent. With the 75/25 mix the ghost will be very transparent while the body will appear more solid.
• Cannon shots and earthquakes: You can make the scene shake, rattle, and roll by recording shot A with the camera still and then re-recording it on the B roll while vibrating the camera with one hand. Together, the A and B shots will simulate violent shaking. Rattle the B roll at rhythmic intervals to simulate heavy gunfire or continuously to mimic an earthquake.

Strictly speaking, side-by-side A/B-roll combinations are not supers, but they deserve mention because the techniques are almost identical. For instance, to allow an actor to play a scene with himself, shoot the A roll with the performer doing role 1 on the left side, while a crew member reads the role 2 lines on the right. Then reverse the process and repeat the scene on roll B.

In editing, use a soft-edge wipe to combine the left half actor with the same actor on the right half, eliminating both shots of the crew member in the process. You'll also need to switch back and forth between the A and B roll sound tracks, so that the actor and not the crew person does all the talking.

You can perform similar tricks by lumakeying, chromakeying and computerized matting, but these are not, strictly speaking, superimpositions. Keep in mind that these techniques do not layer visual B on top of visual A, rather they use digital processing to completely replace the parts of A that lie beneath B.

Compositing like this affords effects that traditional superimposition cannot begin to deliver. On the other hand, inexpensive compositing systems--both stand-alone switchers and computer software--tend to deliver less than perfect results. For a tried and true way to create simple and affordable composite effects, superimposition is hard to beat.

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