How to make a bump map from a texture paint? I want to have a detailed model. The texture paint png file is like this (though these are the details on the mesh, I will create another paint file and want a bump map from that): 

How do I make a bump map from this and have the black lines appear as ridges in the model? This is the model I want to create ridges on: 

Will I need to subdivide the mesh? If so, how many times given the image? And will there be any problems because of the topology? Also, how can I see the effects in real time so that I can adjust the strength of bumps accordingly?
I use an rgb image with 0.5 value (gray) and then plug that into a bump node, and then plug that into the Normal socket of the shader node. I paint in black to sink, white to raise but that can be inverted on the bump node.