Linear Luma Key

The BCC Linear Luma Key filter creates a key from a single channel in the
source. This type of filter is called a luma key, because the key is usually
created from the image luminance, but you can also use any single RGB channel.
You might want to examine the individual channels of the source and use a
channel that provides more contrast between the foreground and background than
the luma channel.

To learn more about this filter, and see a breakdown of the various controls,
please click here.