Downstream Key Tracing
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Here’s the premise: You’ve got an outdoor video scene with things and people in the foreground and a skyline in the background. The sky is blue, but you want to change it to another color, or even replace it all together with another video scene without disrupting your foreground. How do you do it?

If the sky were black to begin with, you could just turn on the luminance key mode on your Panasonic MX-50, Panasonic MX-30, Panasonic AVE-7 or Sony FXE-100 and fill in the black with another video source.

Here’s how you can make that sky black:

Freeze your original video scene onto one of your digital video mixer’s two video busses and select “mix” or dissolve as the transition mode. Feed a live camera that is attached to a copy stand into the other video buss and attach a piece of white paper to the platform of the copy stand (secure it so that it does not slide around).

Perform a partial dissolve between the two busses and with a pencil, start tracing the outline of the sky’s horizon (where the sky ends and the foreground begins).

Now, remove the piece of paper from the copy stand and carefully fill in the area above the line that you traced with a black marking pen. (Or you can cut out black paper in the shape or size you need.) Replace the paper on the copy stand exactly where it was before and return your T-Bar to the buss that displays your original frozen video scene.

Now, turn on your Downstream Key section (“Superimpose Section” on the Panasonic AVE7) and engage External Camera as it’s source. Begin bringing up the level slider in the Downstream Key section until the shape of the sky from your over your original frozen picture.

Select “Full Matte” or “Background Color” as the fill color in the Downstream Key section and as you begin toggling through your different background colors in the background color section, you’ll see the sky changing colors and the foreground remaining unchanged.

If you select Black as the sky’s color, you can record this picture onto tape and then later play that tape back through the digital mixer’s Luminance Key mode. With the Luminance Key in effect, you can key in a new video source over the black sky.

If you select Red, Green or Blue as the sky’s color, you can record that picture onto tape and then later play that tape back through the digital mixer’s Chroma Key mode (if your mixer has it). With Chroma Key in effect, you can key in a new video source over Red, Green or Blue sky, depending on where you set your Chroma Key “hue” control.

A variation of this effect can be the Downstream Key “tracing” of specific objects within a video picture and the shape of that object will be replaced with a different color or a new video scene.

Note: In order to achieve this effect with “moving” video as opposed to a frozen video scene, your video should originally be shot with a camera on a tripod. Otherwise, you will have a somewhat difficult time trying to trace a moving skyline and horizon.

Downstream Keying Using a Character Generator

If you have ever attempted to feed the video output from a stand-alone character generator, such as the Videonics TitleMaker, directly into the Panasonic AVE-5, AVE-7, MX-30 or MX-50’s External Camera input, so that you can key your titles over the mixer’s picture via the Downstream Key (Superimpose) section. You probably encountered a few problems, such as a rolling, jittering, out-of-sync title page.

When ever you connecting anything to the External Camera input, the entire mixer will sync up to whatever comes in through that input. Therefore, whatever signal you feed into the External Camera input, you must make sure it is a very stable signal.

In order to solve this problem, feed your character generator with a stable video source, such as a live video camera or a stand-alone sync generator. This will allow your character generator to lock up on that stable source.

Keep in mind, that since the Downstream Keyer on the Panasonic mixers work on luminance contrast, make sure that your titles you created on your character generator have no drop shadows or outlines. Also, they should be either white letters with a black background or black letters with a white background. Use the Downstream Key section of your mixer to create the drop shadows and outlines, as will as the color of the letters.

NOTE: If you have a Panasonic WJ-MX50 or Panasonic WJ-MX30, you can’t use the sync or genlock output from these mixers to stabilize your character generator. The reason, those outputs are driven by the External Camera’s video input, which you are connecting your character generator.

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