Extreme Contrast for Image Separation

One of the most common techniques for separating parts of an image to reveal only the desired portion is to use a luminance key. A luminance key works with the difference in video level, or contrast, of the clip's signal. You can set your key to either drop out the lightest or brightest portion of your clip or switch it to drop out the darkest portions of the clip first. For example, let's take the black-and-white logo shown in Figure 7.3 (a white image over a black background) and see what happens when you key out different luminance values of that clip:

  1. Place any video clip (original source image) you want for the background on Video Track 1.

  2. Place the logo/graphic clip on Video Track 2 above the original source clip.

  3. Click the clip in Video Track 2 to select it.

  4. Click Setup next to Transparency in the Effect Controls window.

Figure 7.3. Use the Luminance Key filter to drop the black portion out of an image.

graphics/07fig03.gif

or

  1. Select Clip > Video Options menu. Select Transparency from the pop-up menu, or use the keyboard shortcut Ctrl-G (Windows) or Command-G (Macintosh). The Transparency Settings window appears.

or

  1. Right-click (Windows) or Option-click (Macintosh) the clip to open a pop-up menu. Select Video Options from the menu and Transparency from the popup menu.

  2. Select the Luminance Key effect from the Key Effect pull-down menu to drop out the black background (see Figure 7.3). Adjust the Threshold and Cutoff sliders to find the correct levels.

  3. Reverse the values to drop out the white portion of the same image. You see a black image with the logo filled in with the image from the original source clip below, as shown in Figure 7.4.

    Figure 7.4. Reversing the key drops the white portion out of an image.

    graphics/07fig04.gif

There are three ways to view the luminance key effects in the Transparency Settings window, as shown in Figure 7.5:

  • The Black and White box puts a black or white background in place of the part of the image you are trying to key out.

  • The Checkerboard box puts a checkerboard pattern in place of the part of the image you are trying to key out.

  • The Image Display box shows the portion of the video clip (from the footage placed in the video track below the keyed video clip in the timeline) through the keyed-out portion of the clip that contains the effect.

Figure 7.5. There are several ways to view keyed effects in the Transparency Settings window.

graphics/07fig05.gif



Premiere 6. 5 Fundamentals
Premiere 6.5 Fundamentals
ISBN: B000H2MVO4
EAN: N/A
Year: 2006
Pages: 219

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