The Compound Arithmetic effect mathematically combines the clip to which it’s applied with a control layer. The Compound Arithmetic effect is intended only to provide compatibility with projects created in earlier versions of After Effects that use the Compound Arithmetic effect.

Second Source Layer

Specifies the video track to use with the current clip in the given operation.

Operator

Specifies the operation to perform between the two clips.

Operate On Channels

Specifies the channels to which the effect is applied.

Overflow Behavior

Specifies how pixel values that exceed the allowed range are treated:

Clip

Indicates that the values are limited to the allowed range.

Wrap

Indicates that values exceeding the allowed range wrap around from full on to full off, and vice versa.

Scale

Indicates that the maximum and minimum values are calculated and the results are stretched down from that full range to the range of allowable values.

Stretch Second Source To Fit

Scales the second clip to match the size (width and height) of the current clip. If this option is deselected, the second clip is placed at its source’s current size, aligned with the upper left corner of the source clip.

Blend With Original

The effect’s transparency. The result of the effect is blended with the original image, with the effect result composited on top. The higher you set this value, the less the effect affects the clip. For example, if you set this value to 100%, the effect has no visible result on the clip; if you set this value to 0%, the original image doesn’t show through.