Step 4

Adjust levels for "AboveLeft". Select output levels 127 and 0.

Step 5

Create a new image (hereafter called "BelowRight"),  with your Below-lighted photograph for a green channel, and your Right-lighted photograph for a red channel

Step 6

Adjust levels for "BelowRight". Select output levels 128 and 255.

Step 7

Paste BelowRight into a new layer over AboveLeft. Set the new layer's blend mode to "Overlay," and flatten your image.
(Optionally, experiment with other blend modes.  I find "Hard Light" works well for some maps).

Step 8

Fill the blue channel with a light color.  Experiment with the shade; a lighter blue will yield a smoother normal map.

Step 9

Apply NVIDIA's Normal Map filter, using the "Normalize Only" setting. Your normal map should now be finished and ready for use

Step 10

If you need a displacement map, my href="http://66.70.170.53/Ryan/heightmap/heightmap.html" target="_blank">Displacement Map Creator will make one for you.