Matte filters can be used by themselves to create alpha channel information for a clip to composite it against other layers to mask areas of a clip. Matte filters can also be used to make further adjustments to layers with keying filters applied to them. For example, you might want to color -correct only a small area of your image; you can do so with these tools.
4-Point Garbage Matte is similar to the 8-Point Garbage Matte, but it creates the matte using only four points.
8-Point Garbage Matte generates an eight-point mask that you can use to crop out areas of a clip. Eight point controls allow you to "draw" this matte. When you click one of the crosshairs in the filter's controls, the Selection tool changes into a crosshair. You use it to reposition one of the eight points by clicking a new area of the picture in the Canvas window. The Smooth slider rounds off the shape's corners to create rounder mattes. The Choke slider allows you to expand or contract the matte as a whole, and the Feather Edges slider allows you to blur its edges. The Invert check box reverses what's matted and what's transparent, changing it from what's inside the shape to what's outside the shape. The Hide Label check box hides the number labels, which indicate which point of the matte corresponds to which point control of the filter. This matte can be animated as well if what you are trying to matte is moving in the shot. This matte generator has a relative. It's a simpler version of this filter called the 4-Point Garbage Matte. You might want to use the 8- or 4-Point Garbage Matte to create a blur over someone's face to keep his or her identity secret, for example. If you have problems creating the shape with only eight points, you can add this matte to the image again to create a better-defined matte.
Extract creates a luminous matte around the clip. It's similar to a Luma Key. The View pop-up menu allows you to look at the source of the clip (with no key applied), the matte created by the filter, the final matted image, or a special composite of the source, matte, and final image for reference. The slider controls adjust the matte's threshold, tolerance, and softness. The Copy Result pop-up menu allows you to copy the luminance result to your clip's RGB or alpha channel, and the Invert check box allows you to invert the result of this filter. Adding this filter to a clip that is above another clip results in a combination of the images as programmed by the filter. Copying the result to alpha makes for some interesting results, which are quite different from simply superimposing two images. Extract, usually with a garbage matte, is excellent for pulling a key where no keyable color exists. It is also good for cleaning up a difference matte or other key by forcing it to black and white.
Image Mask creates the alpha channel or luminance from another clip you place in its well. Image Mask uses the clip to create a matte for the clip you apply it to. You could draw a black-and-white shape of some kind and then use this shape as a pattern for the matte. The Channel pop-up menu allows you to apply the matte to an alpha channel or luminance level. You can also click the Invert button to reverse the effect. Unlike the Travel Matte composite mode, the Image Mask filter attaches a matte to the selected clip. You can use motion effects to move the affected clip around; the matte stays in position with it.
Mask Feather blurs the clip's alpha channel by an amount specified by the Soft slider. You can add this filter to a masked clip and blur its edges as long as it's added after the matte, such as an Image Mask.
Mask Shape creates a mask shape to use to matte out a clip. A pop-up menu lets you choose from four separate shapesRectangle, Diamond, Oval, and Round Rectangle. The Horizontal and Vertical sliders adjust each shape's size and aspect ratio. The Center control allows you to place the matte anywhere in your picture. The Invert check box lets you reverse what's seen and what's masked.
Matte Choker is used in union with a keying filter to manipulate the key's edges. Instead of using an edge thin slider, try using this filter instead, because it looks more realistic and not as severe. If you move the Edge Thin slider to the right, slightly keyed areas of a clip are lengthened, spreading out the matte and filling in holes in your foreground image that might have been created by the keying filter you're using. Matte Chokers should be applied after a keying filter. Matte Chokers can be effectively used more than once on the same clip. The first Matte Choker might eliminate problems around an edge, but it also might create problems in the foreground image by keying part of it out. If you apply another Matte Choker in reverse, it can fill in these holes to make your foreground image key better. You can continue adding chokers until you are satisfied with the result.
Soft Edges blurs the four edges of a selected image independently by sliding or adding values to each of the four sliders (one for each side of the clip). The Dither and Gaussian check boxes change the quality of the blurred edge, and the Invert check box allows you to toggle between masking the edges and creating a hole in your image, revealing what might be underneath in a lower video track. You can use this filter to create a vignette effect, for example.
Wide Screen creates letterboxed images. The Type pop-up menu allows you to select the aspect ratio of the top and bottom mask using the standard film aspect ratios. Letterboxing helps you achieve a cinematic look. You can adjust the clip as it is revealed by this mask with the Offset slider. You might want to show just the top or bottom of the original 4:3 images, for example. The Border slider moves the top and bottom of the letterbox inward by up to 10 pixels at a time. You don't have to live with black for a border. You can use the Color controls to change the border's color. You can feather its edges by checking the Feather Edges check box. If you do, however, you lose the colored border.