just started using zbrush. at times i find myself lost amongst a plethora of tutorials, taking hours to sometimes find the right one to solve a problem, but this time i’ve exhausted just about every search i can think of. right now, i’m wondering if there’s a way to polypaint on top of a tool which has been uv mapped. for instance, if i uv map a face from photoshop onto a head in zbrush, but later in zbrush i want to place a scar on that face (this is not what i’m doing…this is just a simple example to illustrate), do i have to alter the uv map in photoshop and reapply it again in zbrush, or can i somehow merge the uv map onto the zbrush tool so i can polypaint on top of it? any help would be much appreciated. thanks in advance 
You can convert a texture map to polypaint. The subtool must have enough subdivisions or will lose detail. That can be done the the polypaint menu from tools. Once done you can use the normal polypaint tools.
If you don’t want to convert the texture map to polypaint you have two options:
- Projection master, that is in some way outdated for texture painting.
- Zapplink, that could link you with Photoshop. It will give you an excellent quality and will avoid the degradation of converting from texture to polypaint. But you will need to switch programs for each interaction. Fine if you don’t want massive changes. For the case of adding a scar, unless the area has a very irregular surface, this seems the best method. This tool can be found the the document menu.
- http://docs.pixologic.com/user-guide/zbrush-plugins/zapplink/
you were right, i didn’t have enough subdivisions. works perfectly now. thank you!