The Reaction super tool provides a complete multilayer compositing and 3D effects environment. You can use Reaction to quickly composite and output numerous images that are already processed using other tools, as well as cross over into a 3D environment where you can apply lighting, spatial, visualization, and rendering effects to your scene. You can then use your Reaction output to render your final composition, or use it as an input to other tools in your dependency graph, including another Reaction.