Channel > Arithmetic effect
The Arithmetic effect performs various simple mathematical operations on an image's red, green, and blue channels. Operator specifies the mathematical operation to perform between the value you specify for each channel and the existing value of that channel for each pixel in the image: And, Or, and Xor apply bitwise logical combinations of the specified value; Add, Subtract, and Difference apply basic math functions using the specified value; Max and Min select each pixel in the color channel that is respectively less or greater than the specified value and set it at the specified value. Block Above and Block Below turn the channel off everywhere that it is respectively greater or less than the specified value; Slice turns the channel off where it is below the value specified and turns it on where it is above the specified value.
Clip Result Values prevents all functions from creating color values that exceed the valid range. If this option is not selected, some color values may wrap around from on to off, or vice versa.
