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.)

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.