The normal mixer allows the user to blend existing normal maps with the generated normal map. You can launch the Normal Mixer by first generating a normal map (using any of the source image types) then in the normal map properties you'll see a button called "Mixer". Click it and the Normal Mixer will appear.

All maps are blended in the order they are added to the normal mixer.

The normal mixer allows you to blend an unlimited number of existing normal maps with the ShaderMap generated normal map. Add a mix normal map by pressing the new button and loading it from file. Once the mix map has been loaded you can make changes to the way it is blended. Position (XY): Change the offset position of the normal map. The default position is 0,0 which is located at the top-left corner. Position does not affect the mix map when using the stretch option. Stretch: The mix map is stretch accross the normal map - This method ignores aspect ratio. Position is ignored. 1:1: The mix map is blended using its actual size. Tile: The mix map is blended using its actual size and tiled accross the entire map. Blend Slider: Controls the amount of blending 0-100% Blend Mode: Selects the blend mode from a drop down list. Average Source Overlay Hard Light Vivid Light