Extract Normal Data in Photoshop
This is a photoshop action. It will take an opened normal map (be it a texture or a rendered normal map from your render) and extract the Left, Right, Top, and Bottom data for use in re-lighting a render. The intended use is for using a normal map pass along with the rgb rendered image to re-light or tweak an image using the normal map data pass.
1) Open normal map in photoshop
2) Run this action
3) Action creates 4 empty folders with masks for left, right, top and bottom
4) Create adjustment layers in the respective folders such as curves or color balance to 're-light' your render.