The Alpha Levels tool is one of the tools used for matte cleanup tasks during the keying process. When used as a tool defined by the keyer tool's dependency graph, the Alpha Levels tool applies its effect to the alpha component of the keyer's output. You can clean up the matte by manipulating the input/output luma remapping curve, by adjusting the input and output luma fields or sliders, or by adjusting the lift and gain. The Alpha Levels tool also allows you to invert the matte. The Alpha Levels tool is located in the Alpha tools folder in the Tools tab.

The histogram indicates the distribution of luma values in the input source alpha channel with gray vertical bars along the X-axis. The curve illustrates the resulting luma value. For example, if you drag the part of the curve that represents the darker input grays upwards, the curve over that region becomes lighter.

Since the Alpha Levels tool affects the alpha and is typically applied to the output of a keyer tool, such as the Luma Keyer or the Diamond Keyer, your dependency graph should include, as a minimum, one source and a keyer.

The Alpha Levels tool UI has the following parameters.

• Lift Adjust the Lift to add an overall offset to the matte.
• Gain Adjust the Gain to adjust a scaling factor for the matte. Lift, Gain, Input and Output are animatable attributes—see Marking Attributes for Keyframing.
• Minimum Output slider Drag to remap input blacks to dark gray.
• Minimum Input slider Drag to the right to remap dark grays as black.
• Luma remapping curve View the changes you make in this curve.
• Maximum Input slider Drag to the left to remap light grays as white.
• Maximum Output slider Drag to the left to remap output whites to light gray.