Adobe After Effects CS4 - Manual (Page 457)

451 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
This effect can be used to enlarge or reduce a matte. For example, a white solid area surrounded by black shrinks one
pixel on each side using Minimum and a radius of 1.
The quality setting of the layer doesn’t affect Minimax.
This effect works with 8-bpc and 16-bpc color.
Operation Minimum assigns each channel of a pixel the minimum value for the specified channel within the specified
radius. Maximum assigns each channel of a pixel the maximum value. Minimum Then Maximum performs the
Minimum operation and then the Maximum operation. Maximum Then Minimum performs the Maximum
operation and then the Minimum operation.
Direction The axis along which to scan for values. Horizontal & Vertical scans all directions.
Remove Color Matting effect
The Remove Color Matting effect removes color fringes (halos) from layers with premultiplied color channels. Halos
often occur when an area of partial transparency retains the color of the original background and is composited into
a context with a different background color. Use this effect in conjunction with effects that create transparency—such
as keying effects—to achieve more control over the appearance of areas of partial transparency. (See “
Alpha channel
interpretation: premultiplied or straight ” on page 73.)
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
Original (left), and with Remove Color Matting effect applied (right)
Use Background Color to specify the new background color. To allow this effect to generate color values outside the
range 0.0-1.0 when working in 32-bpc color, deselect Clip HDR Values.
The Remove Color Matting effect was previously known as the Unmultiply effect. The old name refers to the fact that
this effect functions by unpremultiplying color channels—removing the result of the background color being
premultiplied with the color channels of the layer in areas of partial transparency. This functionality differs from Knoll
Unmult and other effects that synthesize an alpha channel from the color channels in an image.
Aharon Rabinowitz provides a video tutorial on the Creative COW website that describes how and when to use the
Remove Color Matting effect.
Todd Kopriva provides a post on the Adobe website that describes the use of the Remove Color Matting and Shift
Channels effects to remove black backgrounds from images.
Set Channels effect
The Set Channels effect copies channels from control layers (source layers) to the red, green, blue, and alpha channels
of the effect layer. For example, you can take the luminance values of the pixels of a control layer and use them as the
blue values for the pixels of the effect layer.
This effect works with 8-bpc and 16-bpc color.