Video Editing: Composites: The Key to Success (page 2)

Back in the day, the word matte referred to an actual, physical piece of glass that had a picture painted on it that the creators of a film wanted to blend with an actual filmed image. You'd think this primitive technique would look incredibly artificial, but, from Ben Hur to Indiana Jones, glass matte paintings were the height of special effects realism.

Today, we can create a matte digitally in our computer. For our example, we're going to use basic matte techniques to create a title in which the video appears through the letters of the title. We'll start by creating a matte in your image editor at DV resolution, 720x480 (see the sidebar for why this is not exactly right). Choose a thick, sans-serif font, like Arial Black, and enter your title using the Text tool. Be sure to make the letters big enough to see video through them: 72 points is a good place to start. Keep the title safe area in mind when you enter your text. Keep the text one color and the background black for this example. Don't worry if the background color is ugly, since we'll make it disappear in a second. Finally, save the file as a TGA or a PNG file, since these formats support automatic transparency.

Place your background video (the moving image you want to see through the letters of your title) into the Video 1 track. Next, add the graphic to the project into the Video 2 track.

You can use the chromakey technique as previously described or the software may automatically make the black area opaque and the text transparent. There is a lot of variability in how different software packages do this, but if you saved an Alpha Channel (see the sidebar) with a TGA or PNG file, your work is done.

The precise technique for creating mattes, masks, chromakey effects and transparency can be complex, but we hope that you can see that the concept is simple. So get out there and find a tutorial or two on the Net and get out your camcorder and start creating some great composites today.

Joe McCleskey is an instructional media specialist.

In essence, you can think of the Alpha Channel as a fourth color channel to go along with the typical red, green and blue that make up a video image. Just as red, green and blue have 256 possible levels of intensity in an RGB image; the Alpha Channel provides 256 levels of transparency that can often be viewed as a grayscale image. Thus, if you want a ghostly image that's only partially visible, you can use the Alpha Channel to mix in the desired level of transparency.

When creating graphics on a computer for display on a television, you will eventually discover an odd distortion effect. If you work with an image canvas that is 720x480 on a computer (with square pixels), when you view the results on a television (with rectangular pixels), it will appear slightly squashed. This will be most noticeable with perfect circles and spheres. The solution is to create your still graphics at 720x540 (or 655x480), and then make sure the graphic is squashed (or stretched) to fill the screen in your video editor.

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