Adjust the luma key effect The following steps assume you have applied the Luma Keyer effect. 1 In the Timeline, select the clip with the Luma Keyer effect. 2 Open the Video inspector. The Effects section of the Video inspector shows the parameters available for adjusting the Luma Keyer effect.
3 To reverse the key and remove white instead of black areas of the foreground clip, select Invert. 4 To adjust the white and black clip values, drag the handles at either end of the gradient thumbnail image. By default, these handles are set to provide a linear key where the luma level linearly controls the transparency of the foreground—100% white is fully opaque, 0% black is completely transparent, and 25% gray retains 25% of the foreground image. Dragging the white and black controls changes the values that result in fully opaque or fully transparent foreground video. 5 To adjust the softness of the edges, adjust the Luma Rolloff control. Higher values make the edges harder, removing any partial transparency, while lower values take advantage of any anti-aliasing or softness the edges might have. 6 To help fine-tune the key, use the View options: Composite (foreground combined with background)
Original (unprocessed foreground) The name of the currently selected View button
Matte (foreground-based alpha signal created by the keyer)
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Composite: Shows the final composited image, with the keyed foreground subject over the background clip. This is the default view.
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Matte: Shows the grayscale matte, or alpha channel, that’s being generated by the keying operation. White areas are solid, black areas are transparent, and varying shades of gray indicate varying levels of transparency. Viewing the alpha channel makes it easier to spot unwanted holes in the key or areas that aren’t transparent enough.
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Original: Shows the original, unkeyed image.
Chapter 12 Keying and compositing
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