I have a simple model that I am doing some tests on. How do I export the texture out?
In paint under brush sliders, “show advanced tools” > “save texmap”
You might want to turn off symmetry, depending on your 3d app.
If you do, then an image containing texture for both halves (twice as wide as it is tall) will be exported, otherwise, a single square image containing half the object, for use with shared UV coordinates will be exported. In this case, you may end up with half the imported model being untextured, so you need to delete that half & mirror the remaining half.
In some apps, this works fine, but on others, it may cause problems such as seams. Especially with Normal maps.
Exporting the maps with symmetry turned off beforehand should just work. The only problem might be if you have to have square bitmaps, in which case, a simple re-size in Photoshop will do the trick.