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TUTORIAL: Compositing: Explosions and light

Posted: Thu, 22nd Apr 2004, 2:08pm

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Simon K Jones

Force: 27955 | Joined: 1st Jan 2002 | Posts: 11683

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Chromanator Tutorials: Compositing

Explosions and light

Sometimes the easiest, most effective solution is easy to miss. If you have tried to composite explosions and other light-based footage using the keying tools, you may have encountered some difficulties.

Even when using the luminosity key, the results tend to be somewhat ‘dirty', with black areas outlining the effect. For example:

There is a simple solution. Rather than using the object tools, instead you should change the composite method from the object's properties. Whilst in the Project View:

  • Select the object and display it's menu.
  • Open the Properties dialog.
  • Change the composite mode to ‘Add'.

This will use a different technique to layer the clip, which involves combining the pixels rather than just placing them over the top of anything underneath. In practice, this means that dark areas will be less prominent than bright areas – therefore black will disappear, but the brightness of the fire/laser/light/etc remains.

It is therefore important to film explosions against a pure black background. Similarly, you must render light-based effects from other programs against a black background if you wish to composite them using Chromanator.

Using the Add composite method for other footage can also yield some interesting results, with a little experimentation. I'll cover some of this in a later tutorial.