Alpha Merger

A color correction filter which lets you merge the alpha information from a separate track into the one the effect is applied to.

Compatibility

Alpha Merger is compatible with Final Cut Pro, Motion, Premiere Pro and After Effects.

Parameters

Alpha Source

Lets you provide additional media to the effect.

When no media has been assigned to this parameter, a standard checkerboard pattern is used to represent areas of the screen where your custom media is missing.

The user interface varies by host:

Drop Zones in Final Cut Pro
Drop Zones in Motion
Video Track Selection in Premiere Pro
Layer Selection in After Effects
This media is used to extract alpha information to be applied to the main clip.

Fitting Method

Controls how media is scaled within the current frame:

Comparing Fit (left), Fill (center) and Stretch (right) methods.

Comparing Fit (left), Fill (center) and Stretch (right) methods.

  • Fit: media is scaled proportionally to fit inside the frame. When the media does not match the aspect ratio of the video frame, some areas remain empty after scaling (pillarboxing or letterboxing).
  • Fill: media is scaled proportionally to fill the entire frame. When the media does not match the aspect ratio of the video frame, portions of the media fall outside the frame and thus are invisible (unless further scaling is applied).
  • Stretch: media is scaled non-proportionally to have the same dimensions of the frame. When the media does not match the aspect ratio of the video frame, this results in all geometric features being deformed.

Alpha Extraction

The following options are available:

  • Native alpha — select this option when you wish to use the alpha channel present in the Alpha Source.
  • Interpret as mask (default) — select this option to interpret the Alpha Source as a mask (matte) track where bright pixel values represent opaque pixels and dark pixel values represent transparency.
  • Use threshold — select this option to process pixels in the Alpha Source through a threshold filter. Additional parameters allow you to control the algorithm.

Threshold

Set to 50% by default.

The luminance value that decides which pixels in the Alpha Source media are transparent, and which ones are opaque.

This parameter is only avaible when Alpha Extraction is set to use a threshold.

Sharpness

Set to 0% by default.

Controls the partitioning of the Alpha Source into opaque and transparent pixels is sharp.

This parameter is only avaible when Alpha Extraction is set to use a threshold.

Invert

Off by default.

Inverts the current alpha channel, as determined by the media supplied in Alpha Sources and the current Alpha Extraction method.

Geometry

Parameters in this group allow you to scale, move and reotate the media assigned to Alpha Source to make sure the resulting alpha information has the desired shape.

Center

A point parameter centered in the frame by default.

Initial location in the frame

While it is possible to change the X and Y coordinates via the inspector, it is far easier to interact with point parameters directly on-screen:

Adjusting Point Parameters in Final Cut Pro
Adjusting Point Parameters in Motion
Adjusting Point Parameters in Premiere Pro
Layer Selection in After Effects

Angle

Set to 0° by default.

Scale X

Set to 1 by default.

The slider is limited to values between 0 and 2 but you can type values between 0 and 0 by clicking on the current value in the inspector.

Scale Y

Set to 1 by default.

The slider is limited to values between 0 and 2 but you can type values between 0 and 0 by clicking on the current value in the inspector.

Opacity

Set to 100% by default.

Softness

Set to 0% by default.