Apple Final Cut Express HD - Manual (Page 788)

788 Part IX Effects
Hard Light
Whites and blacks in the foreground image block the background image. Whites and
blacks in the background image, on the other hand, interact with overlapping
midrange color values in the foreground image.
Overlapping midrange color values are mixed together differently depending on the
brightness of the background color values. Lighter background midrange values are
mixed by screening. Darker background midrange values, on the other hand, are mixed
together by multiplying.
The visible result is that darker color values in the background image intensify the
foreground image, while lighter color values in the background image wash out
overlapping areas in the foreground image.
The order of two clips affected by the Hard Light composite mode is important.
Boxes clip on top Monkey clip on top