Double Vision
An exercise in split screen effects using Video Action for PVR or EditBAY
By Paul M. Grossman

 It’s one of the oldest special effects ever, a split screen. The original Star Trek series featured the effect in no less than three episodes. Recently, ABC’s Fantasy Island re-make showcased Malcolm McDowell playing chess with himself. Several motion pictures use one form or another of the effect, including Big Business, Multiplicity, plus Back to the Future II and III. Disney has used it to produce the Parent Trap saga with a total of five films. Today we will be using Video Action to create a simple split screen effect. You will find there is very precise control over the effect, so with a little creative planning, your talent can move about the set quite freely without destroying the illusion.

The first thing to consider when developing this effect is the staging. Keep in mind that your actor must observe a few rules to accomplish the illusion. First, the threshold of the effect must not be crossed. Second, props that appear in the effect must remain stationary. Lastly, the shots must all have the same lighting and depth of field. In addition, the camera must be steadied on a tripod and must not move from shot to shot.

In this example I have set up the camera to capture three separate areas for the talent to perform, including a hallway, a doorway and a wall. The first thing to do before the shoot is to turn your camera’s autofocus feature off. Instead, at the beginning of the shoot, zoom in on your subject, focus and pull back. This is called pulling focus and it will help keep maintain the depth of field for all your shots. I also shut off my camera’s automatic exposure control option.

The first shot consists of the actor knocking at the door and then making eye contact and waiting. The second shot has the same actor opening the door, making eye contact, and then walking down the hallway.

After capturing the clips, the first thing we want to do is match up the actions. Drag the clips to the timeline and drop an index marker on each clip where the actor first makes eye contact. This gives the illusion that they actually see each other.

Next, move the second clip onto overlay track V3 under the first clip and align the Index markers.

To composite these two scenes, I will apply the Gradient Wizard filter to the clip on track V3. This filter is normally used to create a smooth gradient from one color to another. But is this case we will use it’s alpha channel feature to create a moving transparent matte.

We begin by selecting the Transparency Only option. Already you can see part of the effect.

The option to ‘Repeat Gradient Forever’ is also turned off. Next, I adjust the Gradient Cycle so that we have a blended threshold. This will help hide the threshold if the lighting is not exactly the same in both shots.

Here you can see that the lighting did indeed change in the shots. A hard edge is very clear in the upper left corner. The blended soft edge crossing the door is virtually invisible. Notice the legs?

Next, I drag the hard edge node to the right-hand edge of the image. The soft threshold is lined up with the right-hand frame of the door. This will be the threshold of the split screen. The filter uses keyframes, so the position of the threshold can be moved over time. This will come in handy, because our actor has already broken one of the rules. His hand briefly crosses the threshold of the effect to knock at the door!

At this point I select the Keyframes button so that I can change the position of the threshold. The threshold is dragged to the left hand side of the door frame at the first keyframe. This allows the actor’s hand to safely reach in and knock at the door without disappearing into thin air.

Now I drag the percentage cursor to a point after the knock where the actor’s hand has moved beyond the frame of the door. I then add a new keyframe. By copying the settings of the last Keyframe to the middle keyframe, the position of the threshold will hold stationary until the end of the clip.

The threshold moves across the door from left to right allowing the actor to reach in briefly and knock at the door. Once the threshold is there the door is opened by the actor’s double..

The effect is now complete. With a little planning and imagination, split screens can provide a very unique visual treat.

Watch Your Props

Props that move, like the door in this example, need special attention because they can easily destroy the illusion. For example, I could have keyframed the threshold back over the door again, to allow the actor to follow his double around the corner of the hallway. The only problem was with the door. It’s closed on the first clip and was left open at the conclusion of the second clip. The different positions of the door would have ruined the effect as the actor walked past.

Challenge

Now that you know how to make twins, it not too hard to create triplets. Can you figure out how I did it?

To see a video clip (1274k, mpeg format) click here.
Need a filter for doing splitscreens in Video Action (4k)? Shift click here.

You can find out more information about Video Action for PVR and EditBAY at http://www.dps.com.

The author welcomes questions and comments. He can be reached by email at paul.grossman@dps.com

About DPS Video Action
Video Action for Windows NT is the professional’s choice for broadcast quality digital video editing. Together with DPS’ award winning hardware Video Action delivers a full featured editing solution. The software package comes bundled with all of DPS’ desktop products – DPS EditBay, DPS SparkPlus, DPS Perception, and DPS’ real-time editing solutions the DPS Perception RT and DPS Perception RT3DX. The power of this software is apparent when it is combined with DPS’ award winning hardware. DPS Video Action software makes it easy to move from one DPS hardware platform to another without the need to learn a new editing program or user interface.

About DPS
About DPS – DPS is a leading designer and manufacturer of electronic hardware and related software used for recording, editing and processing broadcast quality video and audio material. The company has three business segments: Broadcast, Professional Post-Production, and Security. DPS products are used throughout the world by television broadcasters, video production studios, post-production facilities and by the computer-based desktop video production industry. Visit our web site at www.dps.com.