Grass Valley EDIUS Pro v.7.20 - Manual (Page 510)

Appendix
488 EDIUS - Reference Manual
[Darker]
0
Compares the background and foreground, and displays the darker color.
[Subtract]
0
Subtracts the foreground from the background so parts of the foreground that are bright become dark.
[Color Burn]
0
Leaves the background color as it is and darkens parts that are superimposed.