Low Poly Model:
To make the low poly mesh its often much faster to start from the high poly model. You may have saved a version, where you have not made all the details yet, to start from. Then its all about removing not useful loops and making the mesh as close as possible to the high poly with using the less possible amount of polys. (When having a mesh that will also deform when animated you have to take that also in account while building the mesh.)
The low poly is also modeled in elements, because then the elements can be used to make different variations of the mask. While building the model you have to avoid more than 90 degree edges because that is not possible for the normal texture to smooth it, however you can model more then 90 degrees if you define smoothing groups or define it with the uvw but that will also give you hard edges. For the mask, I have with 1346 polys a quite high poly count, I made it that high because all the elements are modeled in and the head is usually what's grabs the viewers attention most of the time, so spending more polys here is a useful distribution.
After the model is done a uvw map needs to be made. This basically defines the texture coordinates, it can also be explained like a pattern for sewing.
On the left the mask uvw in the uvw editor and on the right the low poly with the finished uvw and a test pattern applied. Important in the unwrapping process is to give all the polys a equal space in the uvw while having no distortion and also having elements as one uvw piece. That is of course not possible so you have to balance it. For faces where you want to paint details later in Photoshop you may want to have no distortion at all. After all the elements are unwrapped they need to be arranged in the texture layout to use the most pixels of the texture possible. In this case the parts also need to be put in predefined areas of the texture:
This
Layout needs to be used to make the customization of the characters possible. For the body parts a second texture layout is used.
Then the low poly and the high poly get thrown into "xnormal" and out comes a normal texture. Basically the high poly information gets rendered in the normal texture.
This is the normal of the mask. There are already normal details, that were added in Photoshop, in this texture (the dents at the bottom for instance)
Low Poly with the normal texture applied.
Here the finished mask in the unreal editor with the textures and material effects applied. More about that in the next chapters.
Here is the low poly of the full character:
The polycount of this full low poly mesh is at 16530 polys (Note: when talked about polycount it means technical correct tricount)