Face is one of key aspect of creating character. By hosing right face for your character u can change its mood, character, type and how it's going to be seen by different people. However just because it looks different it doesn't mean it has to have different topology. Topology it's the base of the face which we can't see in game. We can see face during game play but not the actual wire and how it's made.
First of all in order to model a face we need a pictures of the person we want to make or the blueprints. Once we got it loaded in our soft it's time to model, since pictures are perspective mode we should also model from perspective mode with same fov as the pictures were taken. One tip is to create camera for each view, thanks to that we don't have to move our perspective camera all the time. Modelling a face it's pretty simple in now days, you can start from sphere in zbrush or mudbox make few subdivisions model face as you go and at the end just retop the geometry to be right for animation and in general.
The retopology, or main topology is the most important thing in this process. It's not how the face does looks like but how its build. For example good topology it's like building with concert fundaments, bad topology it's when we have concert building with wooden fundaments. There is one simple rule in order to create right topology, it's to keep your wire in circle movement. Meaning circling wire around mouth, nose, eyes, entire face from forehead to chin. For example I put some pictures below of it, these are my old and new models that I have worked on.
All these models above are based on one topology. Once you get it right you can make them look as weird as you want and only your skill is limiting you in tems of creating a face exprestion for right character. However I also put there one face that its not finish completly there fore I will need to do some topology adjustments to be fully ready. As you can see my last face of a devil its not properly created around horns. Wire is going straight up ignoring horns. It should go around it just like it happen in other parts of a face.
The image above its showing us how the topology works for each part of face. By creating round wire around mouth we can then open and close the mouth, but also create some wrinkles while we are opening mouth on old characters and accurate skin movement. Same goes for eyes and chicks. When you open yor mouth yo move skin from all around face even from ur chicks and around ears bit. Its not too visible but its happening. The picture below its showing that same thing but from side view.
The reason why we want to have round topolgy its animation of course. Once everything its loopable and easy adjustable we can open our month close do anything. The wire can then be rigged to react as real skin from human face which add more realism and make it easier to do. For example if we had boxy wire just like the one below.
We would run in to a lot of problems because nothing is round there fore in order to open mouth or to do anything would be very hard to rig and animate. Also skin could form incorectly creating bugs and more. Below I put this picture again with some correction that would give us some idea on to how it should looks like in critical areas in order to make it easier in animation and late work.
A,B,C should be rounded.
D is different situation. Some strong heavy characters that are ment to give us feeling that our haracter is unstopable have usually round face, sometimes called ''earth''. Example of that we can see in Gear of War where our character is really big and because of that we can see on his face from mid nose, over chicks to chin he has wrinkles. Lines like that but corrected so they go under the chin would make it possible to do and later rig properly.
For example person above its main character from Gear of War. Thanks to his fat ''earth'' face playing this characters its simply pleasure. Its big body and strong face make it perfect for this game. Loads of great faces we can see in WWE where wreslers are really working on their face expresion.
I also marked there few things. The red lines are symboling wrinkles which we could make from the model above (blue one) and the blue lines are showing us type of face, its got very straight design quite boxy which give us the right feeling. Also thanks to round wire we almost always have wire and enought polygnd to add detail where we need it. For example eye, forhead, and chicks usually in old age or after some damage would have loads of wrinkles, little details or scars. Thanks to making everything round we can add a lot of details and then use normal map to represent it and it will look good since the topology is correct. However sometimes our characters are bick ''wicked'' like the devil above, there we have to strugle and fight throught wire in order to get it right, but by holding to standard round wire method everything should be fine.
Of course in character designs we have more face types than just this one. For example lets take spider man boy. His face is slim, you almost can see bones going out from under his skin. Which make its good choice for that kind of characters because its a fast dramatic person.
Retopology in now days its still most important feature but also one of easiest think to do. Once we create high detail model we can then retop it to add more wire/polys where we have more details, its just fun.
