Manipulating Alpha Channels Using Filters

In addition to using shape and image masks to create transparency within layers, there are also filters you can use to manipulate or even replace a layer’s alpha channel.

For example, all of the keying filters create transparency by generating an alpha channel based on colors or luminance values in that layer. Keying filters are usually used on layers that have no alpha channel information, and they add a new alpha channel to the layers to which they’re applied. For more information on the use of the keying filters, see Keying Filters.

The process of improving a keying effect or of customizing an alpha channel created using one or more shape or image masks may require the use of special filters. Although you can apply any filter directly to a shape or image mask to modify that particular mask’s effect, the filters described in this section modify a layer’s entire alpha channel directly, including the sum total of all masks and other filters that have been applied to that layer.

For example, if you’ve applied a keying filter, you can use the following filters to modify the resulting alpha channel even though no mask appears for that layer in the Layers tab or Timeline.