Need some help converting an alpha picture to a heightmap in photoshop

[waldronate]

I'm not sure how to go about getting something geologically plausible as far as sea floor goes. Painting it by hand (well, cloning it from an Earth map) would probably be the best way.

A bevel would probably work, but it's more for pre-lighted things than bump maps. Doing a couple of bevel layer effects with an additive blend might do what you want.

I'm fond of a tool that's not Photoshop for this sort of thing. A search for "CSU Johnsondale" would turn up some techniques that might interest you if the search things here were working. I used that technique to get the attached image ( I tossed on some random mountains that are undoubtedly in the wrong place for your purposes ). The sea element is basically just a distance transform of the land; an exponential on that might be a little more oceany.