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TUTORIAL: Compositing: Key Grading

Posted: Tue, 27th Apr 2004, 11:42am

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Simon K Jones

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Chromanator Tutorials: Compositing

Key grading

An easily overlooked feature in Chromanator is the Key -> Key Grade toolset. These tools enable you to tweak your footage prior to keying, to aid various keying tools. This can prove useful, for example, if you are using a greenscreen that has not been lit correctly, or if there is a problem with the colour.

For this tutorial I'll use this poorly-lit greenscreen shot:

As you can see, the colours are muted due to the flat lighting, and the greenscreen itself is covered in shadows. If I try to use the Colour Difference key, it leaves an unwanted green haze:

With a difficult shot like this, I should have used the key grade tools before attempting to key out the green. Using only the Super Contrast tool in the Key Grade toolset, I can boost the green considerably:

I don't need to worry about the final output having distorted colours, however, because the Key Grade tools only affect the image before keying. Switching to a non-Key toolset or previewing the frame shows that the colours are still as they should be.

I can now apply the Colour Difference key again:

With the addition of a garbage matte to clean up the areas around the greenscreen and remove a few remaining problematic shadow areas, a very clean composite can be achieved. When rendered, the marine's colours are perfectly normal: