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If your footage has a fair amount of background spill, the last keying plug-in you should use is the Spill Suppressor.
This plug-in is pretty straight forward; select that area of your subject with the offending color and then adjust the suppression amount. Be careful that you don’t desaturate or suppress the spill too much as it can leave a gray ring around your key. The best bet is to see how well the background and foreground elements work with each other before applying this plug-in. In this example, we are going to eventually tint the subject blue, so spill and any other rouge background elements that didn’t make it past the matte choker will look okay.
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| Spill Supressor helps knock out the unwanted spill from your backdrop. Examine the top image to see th before, and the bottom image for the after. |
Instead of adding our background element now, we are going to render out the composition so we can use the alpha channel information in a later step.
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Render the composition in the same format as the original footage (in my case .avi), no compression, and make sure channels are set to RGB+Alpha. Make sure you have audio output turned on as well, unless you want the pleasure of trying to line the audio and video back up later. Save the movie as Hologram_with_alpha.avi.
Sit back and wait as your computer cranks this movie out. Another reason we are rendering this stage out now is that the keying plug-ins can eat up a lot of processor power, and with the layering and effects we are going to add, a faster refresh will help tremendously.
Wow, we’ve certainly covered a lot. Hopefully you understand the principles behind Chroma-keying, different ways a green/blue screen can be created, how to shoot for best results, and how to extract a matte in After Effects.
For the moment, take a breather, grab a vegi-sandwich and a sparkling bottled water and enjoy. When you are finished, come back and finish up the rest of the hologram tutorial.
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