GMask

When pulling a key, use garbage masks (GMasks) to isolate particular areas of an image to include with, or exclude from, the opaque area of the matte. Garbage masks are spline-based objects you draw directly on a clip or image. Depending on what you want to accomplish, you can set the area inside each garbage mask to be either opaque (white), transparent (black), or semi-transparent (any shade of grey).

Garbage masks are useful in many situations, such as when removing unwanted elements like equipment or people from a blue-screen shot, when removing unwanted borders from an image, or when creating complex keys by blending portions of the front and back clips. You can animate the shape of a garbage mask, apply motion blur to it, and even use the Stabilizer to make a garbage mask follow a moving element in a clip.

The following example illustrates keying out an unwanted white border using a garbage mask.

Matte before garbage mask is applied

Matte after garbage mask is applied

You can also apply softness to the edge of a mask using a uniform or advanced gradient. Instead of having an abrupt transition from white to black in the matte, you can control the gradations of grey between the key and the background. For example, softness can compensate for uneven edges of a key by blending the front and back clip. You can apply uniform softness around the edge of a mask or vary the softness range for different parts of the mask.

An advanced gradient adds two splines around the garbage mask. By moving points on these splines, you can control the gradient according to how far the surrounding spline is offset from the garbage mask.

Softness applied around edge of garbage mask spline Image courtesy of Behavior Communications Inc.

Advanced gradient varies softness for different parts of the garbage mask Image courtesy of Behavior Communications Inc.

Access the Garbage Mask menu from the Modular Keyer or the GMask node when you want to use multiple garbage masks or use the Tracer for detailed masks.

Use the Garbage Mask to isolate particular areas of an image to include with, or exclude from, the opaque area of the matte.

To access the Garbage Mask menu, use:

• Batch, then select a node from the Node bin.
• Timeline, then use Batch FX. See Creating Batch FX.
• Timeline, then add Timeline FX from the Effects ribbon. See Adding Timeline FX.
  • When you access the GMask as a Timeline FX, you can enable Use Matte to use the matte input as part of the effect processing.
• Tools, then select from the menu. See Accessing Tools.
• The Modular Keyer, then select the node from the Node bin.

This node accepts a front and a matte clip as input, and outputs a result.

GMask usage notes:

• The Garbage Mask menu includes the Tracer and the region of Interest (ROI) functions, which can also be found in the Modular Keyer.
• The node processes gaps in clips set to No Media as black frames. An unconnected front clip will return an error, while and unconnected back clip will process black frames.
• You can save and load GMask setups directly in Batch or Batch FX.