Apple Final Cut Pro 5 - Manual (Page 1151)

364 Part II Project Interchange
 Multiply: Compares the color values for each pixel of the selected clip with those of
the clip beneath it in the Timeline, and multiplies them together. If the image is
already dark, there is little or no effect. If the image is light, Multiply darkens it. In this
example, the white area of the layered image of brick is rendered totally transparent,
and the brick merges with the floor. Note that shadows are preserved, and the
layered image is lightened and darkened to match the image.
Multiply is useful for knocking out the absolute white values in an image and leaving
all other values of the image alone, and the effect is similar to a luma key on white.
Another good example is to take a scanned image of a page from a book, and use
the Multiply composite mode to knock out the white, leaving only the text itself
superimposed over the other layers of your sequence.
 Screen: Compares the color values for each pixel of the selected clip with those of
the clip beneath it in the Timeline, and multiplies the inverse of each. If the image is
already light, there is little or no effect. If the image is dark, Screen lightens it. In the
example below, the darkest parts of the layered image are rendered transparent, and
the lighter parts become translucent over the image of the musicians.
Screen can be used to knock out the absolute black of a layer and leave everything
else in the clip alone, and the effect is similar to a luminance key on black. Another
good use of the Screen composite mode is to composite stock footage of an
explosion or fire to a background image. Everything that was an even black pops out,
leaving only the explosion superimposed over the other layers of your sequence.