Alpha-channel: some bitmap formats can have transparent areas in them. (For example, the background might be transparent.) There are two types of bitmap transparency:
simple on-off transparency.
This is the only type of transparency available in GIF bitmaps and in
PNG bitmaps up to 256 colors.
"alpha-channel"
or graduated transparency. This is variable between fully transparent
and fully opaque. (Similar to the LX's transparency effects.) Alpha-channel
is available for PNG true-color bitmaps.
Xara LX can import and export both simple and alpha-channel transparency.