Creating believable human face has been one of ultimate goals of many 3D artists. The process of creating an average human face is nothing new or rather a very old topic, however to archive the most realistic and natural-looking possible we have to make the best out of every step we do: from collecting references, planning before modeling,topology, texturing, rendering…etc.
In this study I will only cover part of my research of the modeling process, I will skip through the fundamental things like how to use tools in specific software like Maya/Max or step by step instructions but rather paying more attention to upper level things such as : overall work flow, different approach of modeling, topology, common mistakes …etc as well as all other things that you should put your mind on while working to create a realistic head model.
One fundamental thing you should always aware of is that: always doing research/ planning before digging into doing any actual work. This is critical important for almost anything not just realistic head modeling.
Some master (yes, if there is any) don’t require any reference to work their way up to the final product, but practical-wise and production-wise it is highly recommended or even a must that we must base our work on references, whether it is concept art or photograph…etc. The way we set up references and concept arts have direct influences on our models later. The most important thing in this part is the accuracy and quality of reference photographs, concept arts. If we under estimate or make mistake in this process, we might face serious problems later when the model fit with the front view reference image but does not fit at all with the side view. Other case is that our model look exactly fit in orthographic view but in perspective view it doesn’t look alike the person in reference.
This will consume a lot of time tweaking back and forth, we feel lost and our reference images didn’t come in handy as we expected.
If we are going to take photograph of a real person for references, It is important to take photograph at right angle or else our model will look wrong and we will have to spend considerable amount of time to adjust it. we should also take into account of our camera ‘s focal length. the longer our focal length is, the better reference photographs we have.
Because the longer our focal length is, the closer our view angle to orthographic view ( like front view, side view which we base our modeling on). However, in theory we never get a orthographic reference photograph due to distortion of view angle so the models in 3D always look a little bit fatter than the real person, but this can be solved by additional editing in perspective view. One other thing I like to mention is that we should use even lighting because all the detail will be washed out or become hidden under lighting that is too strong or too low.
Getting reference images into 3D app:
We should not import the raw photo image straight from camera into our 3D software yet, because of the deviation during photograph process we have to check whether these image are exactly fit with each other or not. We should correct our reference images in Photoshop ( using lense profile correction to get rid of the lense distortion) or any other images processing application.
Draw horizontal lines across key elements such as: eyes, nose, mouth and eye browns to check if our references image is consistence and correct-scaled.
3-Edge planning & Topology:
We should always plan our topology before modeling or else we will get lost in maze of edge loops or lost control of our polycount and end up wasting poly on unnecessary parts.We have to sketch out the main shape of the head then base from that we plan our edge structures. Topology is one of key element in 3D modeling in general and especially human face modeling in particular.
Because topology and edge loops play an important part in building up the head volume, face’s characteristics as well as make up what our head model can do/deform in animation.Unlike other parts of character, the head have much more screen time with many close up shots that involve complex facial expression animation like: smile, sad, anger…etc all bring up different shapes and deformations stages of the face.
With a good and smart topology, it is possible for our head model to be able to deform well into to any realistic expression. If we have a messed up topology, our head model can not do a single facial animation and even if it can, the expression will look very un-natural and distorted badly or require a lot of heavy skinning/ deform rigging work. Another plus flint is that nice topology will also make it possible to build the model with less geometry but still look realistic and accurate yet easy to edit and maintain.
3.1- Human Face topology
What is a good head topology? How should we know it is good or bad ? Base on what margin?
In order to answer this question we should go back to our anatomy book and references to look at human face anatomy. Shape of human head, winkles and expressions are all formed and built up by muscles and shape of skull,amount of fat under the skin.The muscles that we need to keep in mind that play important role in forming one person ‘s facial characteristics ( nasolabial folds) are :
– Zygomaticus major and minor
– Levator anguli oris
– Depressor anguli oris
-Levator Labii- Risorious
But these muscles don’t help in determining the face’s shape or the topology of the surface or the nasolabial folds but we should know about them as they are the source of what causing emotion and how facial muscles work underneath the skin:
“Imagine a thick sheet of foam rubber lying on a table, with strings attached to its underside. when one or another string is pulled, part of the sheet slides and wrinkles. The strings are invisible to us – all we see is the wrinkle on the surface. To get it exactly right we must study the outside shape of the sheet, possible also the table, but not the strings themselves”
Steven Stahlberg – “D’artiste: Character Modeling” – Ballistic Publishing 2005
The foam rubber is the skin surface which our model is, and the strings are muscle, and the table is skull. so we should study the movement and shape of the outside skin not the muscle. So we decide the topology base on the major wrinkles which is formed by facial muscles. so a good knowledge about muscle and facial anatomy is a bonus but our head model might not look realistic if we try to plan the edge structure on exactly every muscles and wrinkles, it would lead to a dead end. it ‘s better for us to exaggerate the wrinkles on the reference images and build our topology upon that.
This is a basic example of how should we sketch out our topology on reference images, we start with the most identical wrinkles then building up intersected edge flows from that. Since most of human face are about 99 % similar to each other in anatomy, so the topology would not change dramatically. These are some good and bad examples of face topology:
Looking at those good topology examples,you can see that each model has a slightly different topology but they still base on the same concept of edge flows and plannings.
” Humans are genetically similar to 99.97 percent or something like that. Yes the lines in the face look different, but we all have the same underlying topology, the potential for those lines. It’s like lines in the hands of our palms, all slightly different but basically very similar – for instance you’ll never see someone with the lines going in the opposite direction, from the thumb to the pinkie.”
Steven Stahlberg – “D’artiste: Character Modeling” Ballistic Publishing 2005
“On the guy, the typical doubled-semi-colon shape that’s created by the nasolabial folds as they run into the chin, together with the next wrinkle parallel to it. Almost every single person on the planet shows something quite similar. (Although a few have the nasolabial fold hooking up a bit lower on the chin.”
Steven Stahlberg at www.cgsociety.com
It ‘s also better to know that there is no such looping structure in our human face, as we can see in those reference, breaking our face structure into edge loop is only for the sake of sufficient and simplification of polygon topology. So that the face’s topology in 3D technical term is approximated and there is no absolute single perfect topology for head, it ‘s depended on our reference and purpose of the model.
3.3- Modeling rules:
The rule for human face modeling is the same as other objects:
-Keeping a suitable tris count (not too high for easy editing , not too low for better model definition).
– Use quad as much as possible and use triangle when necessary, triangle are not recommended but it doesn’t harm having a few triangle to terminate our edge loop to avoid adding extra unnecessary loops , but keep in mind the fact that the model might not deform nicely when animated and smoothed but it will save us unnecessary edge loops and faces.
– Avoid poles (where vertex share more than 4 edges, it’s impossible to avoid pole in our model but we should hide these at those area that are less seen in the model because the areas that have pole are not smoothed properly)
– These are some area that usually have pole and they are acceptable.
Polygon should always be as chubby or square, no long thin nor diamond shaped (some of these are acceptable to form wrinkles ). Square & chuppy polygon are hold up nicer when being deformed.
– The edge direction should not run across the curvature line of surfaces.
– The worst case is topology running at 45 degrees to the curvature line of the surface form those diamond shape deforms which will look terrible later in render and smoothed.
” The most difficult part is finding the balance between having enough detail to achieve what is needed and building as light a model as possible”
Francisco A.Cortina “D’artiste: Character Modeling”- Ballistic Publishing 2005.
The more edge and polygon we have, the more accurate and realistic our model is but the more difficult we can edit and maintain it. This apply for both still image and animation. With still image sometime it’s okay but it’s a good practice to keep our model as necessary light and low res as possible. If we want to have extra details, the key thing lies in the texture part. Especially normal and displacement map.
Main topology lines in head model:
Green lines are mostly to help polygon flows form the shape of the body part base on surface curvature while Red line will play their role during particular extreme expressions.
Note: Red line loops will varies in different head models base on animation requirements, the more extreme expression & wrinkles the face have, the more extra red lines will need to add to the face to build up the deformation properly.
There are many different ways of modeling a human head, everyone find their own comfortable way to model. These are some main methods that I sum up: