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Luma Key
The Luma Key effect keys out all the regions of a layer with a specified luminance or brightness. The layer's quality setting does not influence the Luma Key effect.
A white background of the original (left and center) is removed using Luma Key (right).
When the object you want to matte has a markedly different luminance value than its background, you can make the background value transparent by keying it out. For example, if you want to create a matte for musical notes on a white background, you can key out the brighter values; the dark musical notes become the only opaque area.
To key out a luminance value:
- Select the layer, and choose Effect > Keying > Luma Key.
- Select a Key Type to specify the range to be keyed out.
- Drag the Threshold slider on the Effect Controls window to set the luminance value on which you want the matte to be based.
- Drag the Tolerance slider to specify the range of values to be keyed out. Lower values key out a smaller range of values near the threshold. Higher values key out a wider range of values.
- Drag the Edge Thin slider to adjust the width of the keyed area's border. Positive values make the mask grow, increasing the transparent area. Negative values shrink the mask.
- Drag the Edge Feather slider to specify the softness of the edge. Higher values create a softer edge but take longer to render.