Extracting a Range of Colors

The second technique used to create a key is extracting a range of colors in the key-in image. Use this technique for clips where the color you are extracting contains impurities.

To build a key by defining a color range, you can use one of several color models, each of which interprets the key-in image differently and gives a slightly different result.

Once you choose a color model, you set a range of colors to become partially transparent to soften the transition between the front and back clips in the composite image. This is called the softness range. All pixels in the front clip within the softness range are gray in the matte.

After setting the softness range, you set a range of colors to be keyed out. This is called the tolerance range. All pixels in the front image within the tolerance range are black in the matte. The tolerance range must not be too large or the edge of the composite will be too hard and the subject in the front image will appear to be pasted into the background.