Ok, so I have my high rez mesh, all polypainted, but no UV’s and 9 million polygons. I Re-topo’d and exported a 4k triangle version and unwrapped it, but now cannot for the life of me figure out how to get my Polypainting onto the UV’s of the low rez version of the head. I generated a Normal map in ZMapper between the two, this worked fine, is there a similar way with polypainting? Also, when trying to generate a Cavity map I get absolutely NOTHING from Zmapper, just a grey version of the low rez mesh, despite capturing the high rez mesh, going to the low rez, opening Zmapper and clicking “generate Cavity map”. Any help on either of these problems would be excellent.
The HiRes and the LowRes share the same UV, go to the highest subdivision and go to Tool --> Texture --> Col->Txr
and the color data from the High Res will be mapped to the UV.
Subdivide the low-res version to have as many polygons as the high-res version. Append it as a SubTool and then use Tool>SubTool>Project All to transfer sculpt and color to the new model. (Make sure that Draw>Rgb and Zadd are turned on.) You may need to use the other sculpting tools (such as Zproject) to fix small problems here and there.
After that, apply a blank texture to the model and use Col>Txr to transfer the polypaint to the texture. Flip and export that, then go to level 1 and create your cavity map.
ok, i gave your instructions a try, and it worked, right up to the Color >texture. It doesnt seem to have projected the polypaint onto the low rez version, therefore, when i capture the color, all it does is give me a nice blank texture.
The resolution of polypaint is one pixel per polygon, so if you went to the LowRes, it will look all blurred up.
You can convert the color data from the HiRes to the UV as texture, then use that texture to map the color on the LowRes.
Under the condition that they share the same UV.
well the problem at the moment is that they do not share UV’s, and all of the methods that I know of to bake the texture to the other UV’s are not working. GUV tiles baking from hi to low rez in Xnormal is not working, and Sub-tool project all is not projecting the polypaint from my high rez to my equally hi rez unwrapped version (it is only projecting the mesh details).
OK, Ill be frank, I just dont know what your problem is anymore, so I`ll tell you on how I go with my work flows.
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Sculpt and Paint the thing.
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Start Retopo, make sure project is turn on.
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When making Adaptive Skin, push your density to as high as you need.
By doing so, you`ll get a mesh with correct topology, LowRes + HiRes Divisions, and polypaint data all in a single new mesh.
UV can be done at any time after Retopo was done.
Hi Xenier 
I like Aurick’s method but you say you’re having problems. Try this:
Use Uv Check to verify that you have functional UVs.
Verify that Zbrush is in fact capable of showing ANY texture for you.
People always forget to turn the RGB intensity back up before using clr -> txr. This should be at 100 and RGB should be selected.
Try a different scene and get the workflow down with some spheres or cubes or something.
Thanks JBuck, i’ll give it a shot with some simple shapes. All else fails, I may just have to Re-topo again.
Success! a simple re-topo fixed everything!