Chroma Key

What it does: Chroma Key mixes two shots together by converting a selected color in the source shot into transparency. Typically, the source is shot with a green or blue background and then the Chroma Key is applied to replace the background.

How to use it: Chroma Key requires two clips - a foreground clip and background clip. Apply the Chroma Key to the foreground clip.

  1. Select the background color with the Color picker by sampling a color from the background in the clip.  This should be an average value - somewhere between the darkest and the lightest.
  2. Calibrate it with the Sensitivity control.
  3. You might also adjust the Color Range if you'd like to widen or restrict the range of color used in the background.
  4. Set Erase Spill to remove any chroma color bleeding from the background.
  5. If you still have problems with borders, use the Soften and Shrink controls to clean up the boundary between the foreground and background image.
  6. Then, place the background clip on a second track so it displays wherever ChromaKey renders the foreground clip transparent.

  • The Color control sets the chroma key color. Use this to sample the background color. If the background has an uneven intensity, pick something in the middle.
  • Sensitivity sets the sensitivity of the keyer. Adjust this to find the best threshold to separate out the background. You might enable the Show Mask option so you can more easily see the mask.
  • Color Range adjusts the hue range accepted by the keyer. This is useful if the chroma paint is inconsistent. Increase this to allow a greater range of color.
  • Erase Spill removes key color from the image. Often, there is some background color reflecting off the sides of the subjects or bleeding through translucent objects (hair is a good example.) When this image is then keyed over a different color background, the color bleed becomes very apparent. Turn up the Erase Spill control to subtract out this color. Don't overdo it, though, because at higher settings it can remove more color than you might want.
  • Soften blurs the edges of the mask.
  • Shrink reduces the size of the visible portion of the foreground image. This is useful for cleaning up the edges of the mask.
  • Enable the Show Mask option to see the image as a black and white mask. This makes it much easier to calibrate the color key.
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