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.
 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.
 "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.