Apple MA434Z/A User Manual - Page 696

Filtering Keys: The Correct Way The problem with the three examples above is that the keying node, in this case Keylight, is being made to do too much-by having to simultaneously key, suppress spill, and composite within the same node, there is no good place to apply a filter. The solution is to pull a key for purposes of creating a mask, but to use other nodes to perform the actual compositing. In the following example, the Keylight output parameter can be set to either "comp" or "on Black." The image and alpha that's output from the Keylight node can then be filtered, and the filtered result composited against the background using a simple Over node. In general, it's good practice to use the Primatte and Keylight background inputs as test composites only, to be able to see how the key is looking while you're tuning it. Once you're done pulling the key, you can rewire the output image into a composite using an Over or a KeyMix node. This method of working gives you several advantages: • You can apply filters and effects to the foreground material. • You can transform the foreground material. • You can color correct the foreground material. Keying DV Video DV footage, which is compressed with a 5:1 ratio as it's recorded with 4:1:1 (NTSC) or 4:2:0 (PAL) color sampling, is less than ideal as a format for doing any kind of keying. This is due to compression artifacts that, while invisible during ordinary playback, become apparent around the edges of your foreground subject when you start to key. With a high-quality DV camera and good lighting, it's possible to pull a reasonable key using DV clips, but you cannot expect the kind of subtleties around the edges of a keyed subject that you can get with uncompressed or minimally compressed video (decent) or film (best). For example, while you may be able to preserve smoke, reflections, or wisps of hair when keying uncompressed footage, with equivalent DV footage this probably won't be possible. 696 Chapter 24 Keying