Arithmetic Group:

Standard numerical operations.

Addition:

The source is added to the destination and replaces the destination. Addition mode is very simple - the pixel values of the upper and lower layers are added to each other. The resulting image is normally brighter. The equation can result in color values greater than 255, so some of the light colors may be clipped to the maximum value of 255. Math formula is the same as that used by SVG but slightly different than Gimp.

Subtract:

Subtract mode reduces the pixel values of the upper layer by the pixel values of the lower layer. The resulting image is normally darker. You might get a lot of black or near-black in the resulting image. The equation can result in negative color values, so some of the dark colors may be clipped to the minimum value of 0. Math formula used is different than that used by the Gimp "Default" version, but you can get the same as the "Legacy" version if you switch the 2 tracks or use the overlay plugin and switch to Top first. There is no SVG equivalent.

Multiply:

The source color is multiplied by the destination color and replaces the destination. The resulting color is always at least as dark as either the source or destination color. Multiplying any color with black results in black. Multiplying any color with white preserves the original color. Math formula is the same as used by SVG and Gimp.

Divide:

Divides source color by destination color. If the source color is white, the result color is the underlying color. The resulting image is often lighter. Math forumula is different than that of Gimp, but by changing the order of the Source and Destination tracks you can get the same results in some cases (this is true for the original Cinelerra version also). There is no SVG equivalent.

Replace:

Replace mode will cause any existing destination to be replaced by the source media. Math formula used is the same as used by Gimp; there is no SVG equivalent.