Keying effects

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

The Color Difference Key effect creates transparency from opposite starting points by dividing an image into two mattes, Matte Partial A and Matte Partial B. Matte Partial B bases the transparency on the specified key color, and Matte Partial A bases transparency on areas of the image that don’t contain a second, different color. By combining the two mattes into a third matte, called the alpha matte, the Color Difference Key creates well-defined transparency values.

The Color Difference Key produces high-quality keying for all well-lit footage items shot against a bluescreen or greenscreen and works especially well with images that contain transparent or semitransparent areas, such as smoke, shadows, or glass.

This effect works with 8-bpc and 16-bpc color.

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

The Color Key effect keys out all image pixels that are similar to a specified key color. This effect modifies only the alpha channel of a layer.

This effect works with 8-bpc and 16-bpc color.

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

The Color Range effect creates transparency by keying out a specified range of colors in either the Lab, YUV, or RGB color space. You can use this key on screens that consist of more than one color or on bluescreens or greenscreens that have been unevenly lit and contain different shades of the same color.

This effect works with 8-bpc color.

The Difference Matte effect creates transparency by comparing a source layer with a difference layer, and then keying out pixels in the source layer that match both the position and color in the difference layer. Typically, it’s used to key out a static background behind a moving object, which is then placed on a different background. Often the difference layer is simply a frame of background footage (before the moving object has entered the scene). For this reason, the Difference Matte effect is best used for scenes that have been shot with a stationary camera and an unmoving background.

This effect works with 8-bpc and 16-bpc color.

The Extract effect creates transparency by keying out a specified brightness range, based on a histogram of a specified channel. It’s best used to create transparency in an image shot against a black or white background or against a background that is dark or bright but consists of more than one color.

This effect works with 8-bpc and 16-bpc color.

In the Effect Controls panel, the Extract effect displays a histogram for a channel specified in the Channel menu. The histogram displays a representation of the brightness levels in the layer, showing the relative number of pixels at each level. From left to right, the histogram extends from the darkest (a value of 0) to the lightest (a value of 255).

Using the transparency control bar beneath the histogram, you can adjust the range of pixels that are made transparent. The position and shape of the bar in relation to the histogram determine transparency. Pixels corresponding to the area covered by the bar remain opaque; pixels corresponding to the areas not covered by the bar are made transparent.

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

The Inner/Outer Key effect isolates a foreground object from its background.

This effect works with 8-bpc and 16-bpc color.

To use the Inner/Outer key, create a mask to define the inside and outside edge of the object you want to isolate. The mask can be fairly rough—it doesn’t need to fit exactly around the edges of the object.

In addition to masking a soft-edged object from its background, Inner/Outer Key modifies the colors around the border to remove contaminating background colors. This color decontamination process determines the contribution of the background to the color in each border pixel, and then removes that contribution—thus removing the halo that can appear if a soft-edged object is matted against a new background.

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

Linear keys create a range of transparency across an image. A linear key compares each pixel in the image to the key color you specify. If the color of a pixel closely matches the key color, it becomes completely transparent. Pixels that don’t match as well are made less transparent, and pixels that don’t match at all remain opaque. The range of transparency values, therefore, forms a linear progression.

The Linear Color Key effect uses RGB, hue, or chroma information to create transparency from a specified key color.

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

In the Effect Controls panel, the Linear Color Key effect displays two thumbnail images; the left thumbnail image represents the unaltered source image, and the right thumbnail image represents the view you’ve selected in the View menu.

You can adjust the key color, the matching tolerance, and the matching softness. The matching tolerance specifies how closely pixels must match the key color before they start becoming transparent. The matching softness controls the softness of edges between the image and the key color.

You can also reapply this key to preserve a color that was made transparent by the first application of the key. For example, if you key out a medium-blue screen, you may lose some or all of a light-blue piece of clothing your subject is wearing. You can bring back the light-blue color by applying another instance of the Linear Color Key and choosing Keep This Color from the Key Operation menu.

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

The Luma Key effect keys out all the regions of a layer with a specified luminance or brightness. The quality setting of the layer doesn’t influence the Luma Key effect.

Use this effect if the object from which you want to create a matte has a greatly different luminance value than its background. For example, if you want to create a matte for musical notes on a white background, you can key out the brighter values; the dark musical notes become the only opaque areas.

This effect works with 8-bpc and 16-bpc color.

The Key Cleaner effect recovers alpha-channel detail from a scene keyed by a typical keying effect, including recovering detail lost due to compression artifacts.

The Advanced Spill Suppressor effect removes color spill on a foreground subject from a colored background used for color keying.

The Advanced Spill Suppressor effect has two methods for spill suppression:

1. Standard - The Standard method is simpler, automatically detects the dominant key color, and requires less user input.
   
2. Ultra - The Ultra method is based on the spill suppression in the Ultra Key effect in Premiere Pro. See the Ultra Key section in Premiere Pro for details about the Ultra Key.
   

An easy way of applying these effects is by using the Keylight + Key Cleaner + Spill Suppressor animation preset.

After Effects includes several built-in keying effects, as well as the Academy Award–winning Keylight effect, which excels at professional-quality color keying. For information on the Keylight effect, see its documentation in the folder in which the Keylight plug-in is installed. (See Plug-ins.)

For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.

See Third-party plug-ins included with After Effects.

Follow the steps below to apply the Keylight effect with the Key Cleaner and Advanced Spill Suppressor effect:

1. Use the Keylight + Key Cleaner + Advanced Spill Suppressor animation preset (in the Image-Utlities folder under Animation Presets) to apply the three effects in order to the layer.The Advanced Spill Suppressor effect is turned off by default to allow you to sample the key color in the Keylight effect or if the footage does not have any color spill to be removed.
2. Use the Keylight effect's Screen Colour eyedropper to sample the key color from the layer in the Composition panel. Adjust other Keylight effect settings as you normally would to get the best results.
3. Turn on the effect switch for the Advanced Spill Suppressor effect to remove color spill from the scene, if required.
   

Follow the steps below to apply the Key Cleaner and Advanced Spill Suppressor effect to a keying effect other than the Keylight effect:

1. Apply the keying effect to the layer.
2. Set the effect to the equivalent of the Keylight effect's Indeterminate Result setting, so that the keying effect gives the full RGB result without attempting to perform its own spill suppression.
3. Apply the Key Cleaner effect after the keying effect.
4. Apply the Advanced Spill Suppressor effect after the Key Cleaner effect.