The Compound Arithmetic effect mathematically combines the layer to which it is 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. Using blending modes is usually more effective than using the Compound Arithmetic effect.

This effect works with 8-bpc color.

Second Source Layer

The layer to use with the current layer in the given operation.

Operator

The operation to perform between the two layers.

Operate On Channels

The channels to which the effect is applied.

Overflow Behavior

How the effect remaps values that fall outside the grayscale range of 0-255.

Clip

Values above 255 are mapped to 255. Values below 0 are mapped to 0.

Wrap

Values above 255 and below 0 are wrapped back around into the 0-255 range. For example, a value of 258 wraps around to 2, a value of 256 wraps around to 0, and a value of ‑3 wraps around to 253.

Scale

The maximum and minimum values are remapped to 255 and 0, and intermediate values are stretched or compressed to fit within this range.

Stretch Second Source To Fit

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

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 layer. For example, if you set this value to 100%, the effect has no visible result on the layer; if you set this value to 0%, the original image doesn’t show through.