JANUARY 02, 2003
Inner Outer Key
Your Chromakey alternative
by Stephen Schleicher

In the past I have proclaimed how the Color Difference Key in Adobe After Effects was the best all purpose keyer in the After Effects gallery of plug-ins. There are some limitations to the Color Difference Key effect; especially when it comes to keying whispy, smoky elements, or when you don’t have a chromakey background to begin with. In many cases, the Inner Outer Key effect will be able to help you out.

The Inner Outer Key effect is one that many people shy away from when they see that it doesn’t approach keying in the same manner as other keying plug-ins. Instead of selecting a color or color range, the Inner/Outer Key uses user defined masks to define the areas that need to be keyed.[an error occurred while processing this directive]The Outer mask that is created can be thought of as a garbage mask - simply define that area outside of the foreground subject that contains the background color.

The Inner mask is a way of defining the color ranges of the foreground subject. You don’t always have to make the Inner mask conform to the exact shape of the foreground subject, but it can help by reducing the amount of "extra" work you have to do after telling After Effects which masks are which.

It is fairly straight forward process. Let’s take a look at two examples.

In the first example, we have some smoke against a blue screen. With the traditional Color Difference Key effect, you run the risk of keying out the whispy portions of the smoke, leaving only the main smoke column.

The smoke foreground layer against a blue backdrop.


With the Color Difference Key, the smoke almost completely keys out making it invisible against a colored background.


By using the Inner Outer Key, the fine details of the smoke plume are maintained.

The inner mask (red) and the outer mask (yellow) define the range that After Effects will key out.


The smoke keys much better than the Color Difference Key, creating a much better final effect.





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