Learning Vegas: Compositing modes and transparency

The Compositing Mode button determines how the transparency in a video track is generated. Because lower tracks show through higher tracks, it is the compositing mode of the higher track that determines how much of the lower track shows though. The compositing mode of the lowest video track adjusts its transparency against the background.

The mode can be selected by clicking the Compositing Mode button and choosing a mode from the menu.

The following examples demonstrate how each of the compositing modes would affect two simple tracks. Track one is a generated media event with a transparent edge, and track two is a DV clip.

Mode Description Example
Multiply (Mask) Merges the colors of the tracks.
Source Alpha Uses the alpha channel to determine transparency.

The compositing mode is based on the alpha channel characteristics of an event or media file. If no alpha channel is present, the Source Alpha mode has no effect.

Add Combines the color values in the composite group.
Subtract Subtracts the overlay color values from the background.
Cut Cuts out the overlay color values from the background.
Screen Multiplies the inverse of the overlay color values with the background color values. This makes overlay colors weaker and less present and results in a lighter video image. The opposite of this mode is Multiply.
Overlay Heightens contrast by using Multiply mode on darker colors and Screen mode on lighter colors.
Hard Light Adds overlay colors as if the overlay were lit by a bright, focused spotlight.
Dodge Brightens the background based on the overlay color values.
Burn Darkens the background based on the overlay color values.
Darken Compares the overlay and background pixel by pixel and selects the darker color value for each pixel.
Lighten Compares the overlay and background pixel by pixel and selects the lighter color value for each pixel.
Difference Compares the overlay and background pixel by pixel and subtracts the darker color value from the lighter color to generate a new color value.
Difference Squared Remaps color values along a parabolic curve. The color values of the layers in the composite group are subtracted, and then the subtracted values are squared.

The resulting image will have less extreme changes in color values as the colors approach black (RGB 0,0,0) and more extreme changes in color values as colors approach white (RGB 255,255,255).

Drag the Level slider in a video track to control the transparency or blending of each track. Left is 100% transparent and right is 100% opaque. You can also double-click the percent to enter a specific numeric percentage

When you click the Parent Composite Mode or Compositing Mode  button and choose Custom from the menu, you can use plug-ins to customize compositing.

The included Displacement Map, Height Map, and Bump Map plug-ins can create interesting lens, mirror, water, fire, and other light-bending effects.

Plug-In Description
Displacement Map Uses the parent image as a guide to offset the pixels in the composited child tracks along the horizontal and vertical axes.

The X and Y offsets are independently encoded in the image color channels.

Height Map Uses the parent image as a guide to make the pixels in the composited child tracks appear closer to or farther away from the viewer.

The gradient of the image in the parent track is used to determine the amount of offset for the image displayed at that location, in much the same way light bends through a lens.

Bump Map Uses the parent image as a guide to add texture and lighting to the composited child tracks.

The texture of the bump map is applied to the composited child tracks: light sections of the map represent high areas, and dark sections represent low areas.

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