Creating Normal and Specular maps for use in unity can be a pain if you don't have the correct software, and it can be costly. Crazy Bump is a very simple to use piece of software and is available to download for both Mac and Windows, however it is only available for Windows trial for free and can set you back $299 for a full pro licence. But there is good news for Mac users. The nice people at Crazy Bump have been working on a Mac version of the software and have released a Beta version for download.
The good part is the fact that it looks like they are not going to finish the software so the free beta download is available to mac users (It hasn't been updated in the last two years). This excellent piece of software can quickly and easily create maps from Diffuse textures, Height Maps and Normal Maps. It allows you the change the settings via simple sliders and view your changes on a 3dimensional object in real time. It also allows you to export several different map types.
If you are working on a Mac computer then I definatley reccomend you try this out.