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:
4.1- Polygon Modeling:
Polygon modeling is the most popular, essential and straight forward modeling method.Within polygon modeling, it has different ways :
– Start from a primitive shape ( cube or sphere…etc) : some people start by modifying primitive basic mesh like cube or sphere. We block out the overall shape of the head first and delete some unnecessary face and edge loops to form a basic topology. Then we start going into detail modeling by adding more edges and faces around areas like eyes, nose, mouth….etc
Start from curve/lines and separated part: Some people prefer to draw curves (mentioned in above example as green lines) that run along the surface’s curvature of body part in reference images, these lines together will form a basic head shape. After all, extrude out polygon around the lines and start building separated parts of the face, connect them together when done and carry on editing those gap (adding red lines) to form a completed face.
Polygon modeling let us have direct control over edges, faces and vertices, it’s fast and easy to keep track of modeling process however it require a lot of editing work and sometime it does not work efficiently with surface that need high smoothness and accuracy. However with human head modeling it work best in my opinion.
4.2- Sub-D Modeling:
SUB-D : this can be also called polygon modeling. Not many people choose this method to work with.
At the beginning, it is the same as polygon modeling, once we have our basic head model, we can go into detail by adding edge flow to areas that have more detail (need more edge / vertices) than other areas like eyes, nose and lips.
N-gone and unterminated edge loop are allowed at the base mesh because we will have to smooth the whole model to convert all the polygon to quad. The advantage of this method is the hierarchy workflow it allow we to easily edit the vertex at base-level if we want to change the overall shape of the head while don’t need to worry about the detail/extra edge loops created by those detail areas
The other advantage is the low res version of the model doesn’t need to be perfect in topology when we go to higher level, all these N-gone will be all quad and smooth without losing any detail.
4.4- Zbrush/Mudbox Sculpting Modeling:
Sculpting: an alternative way to modeling a human head is using 3D sculpting software like Zbrush or Mudbox, we can start from very basic primitive base mesh then we start sculpting and adding detail to the model. After you have done with the sculpting process, we can use the retopology the head whether it can be done in Zbrush/Mudbox or your 3D package to create a lighter/topology-correct model but still keep the similar look of our high res sculpture model.
The advantage of this method is that we can detail our head model with millions of polygon, in the plus side: the process of modeling and topology is separated so we can concentrate on one thing at a time, modeling first, topology later! Derived from the high res model we can generate normal map, cavity map, displacement map, etc. These textures will help us a lot in texturing works later.
The disadvantage are: This method will take a lot a time, we have to create both super high res model and low res model. In addition we need to have a good sculpting skill in order to sculpt a good high res model with details. But these are only few disadvantage I can find for this method, overall I think it is really good and being used by many artists nowadays, sculpting has been becoming mainstream day by day
Among all the modeling method I mentioned above, I find myself comfortable with the basic polygon modeling which I will use to create the base mesh in Maya and then i will bring it into Zbrush for sculpting and re-topology. Then I can export the lowest-level mesh in Zbrush back in to Maya and apply a displacement map & normal map generated in Zbrush to make it look like the original high res model.
5- Details & tips:
However, despite of what modeling method we are using. Below are some tips & tricks and details that we should pay attention to.
5.1- Eye areas
“Eyes are the window of the soul” they said, eyes are the critical important element in painting as well as 3D. Viewers always look at the eyes of character first. It’s the eyes that make the most characteristic out of character’s face. So it is never redundant when we spend extra time for the eyes.
It is better to use a sphere as reference to model the eye lids or else they will look unnatural and intersect with the eyeball. The eye lids are decided mainly by two curves that formed by upper and lower eyelids. We should also have an extra edge loop inward to make the thickness of the eyelids. The angle of the eye lids’ thickness is also have to pay attention to, so that they can catch light better.
The eye’s canthus should be modeled with real polygon (i.e.: not just texture / bump map) or else our eyeball won’t fit in the eye holes. Some people make eye’s canthus separately from the face, but this will make it look like having dirt in the eye’s comer so it’s better to having everything as one union mesh object.
It is not recommended when making an absolute circle edge loop around eye areas, instead we should have a line go out from the outside eyes corner which will help building up the volume of the upper eyelid .These small detail seem not to be noticeable from far distance, but in close up scene they make the eyes look much more realistic and soulful.
5.2- Eye Balls
Many people underrate this part and they only use one single simple sphere for the eye ball, this make the eye look robotic and dollish. Looking at realistic eyeball, we can see that the eyeball look much deeper and glossier.
The key is we have to mimic the real anatomy of the human eyeball. The most used method in modeling realistic eyes nowadays is breaking the eye ball into two separate part: cornea and eyeball.
– The cornea is like a sphere but more bent forward at the center, and it’s transparency with only catch specular, reflection and even refraction.
– The eye ball is a sphere but sunken inward at the center to form iris.
This detail modeling can make our model’s eyes believable.
The water part between the eye lid and eye ball should also be modeled as separated mesh object to have realistic looking water ring around the eyes.
5.3- Eye lashes & tear
It is important to get the natural shape of eye slashes right. The shape is determined by the many features of the eyes lashes.
“An important thing to remember is to get to correct amount of bunching and randomness in both length and placement. The lower lid’s lashes tend to bunch in smaller numbers, while the upper lid’s lashes bunch in greater numbers. The small membrane on the inner corner of the eyelids, or the ‘caruncula lacrimalis’, is one of the most important elements of the eyes.”
Francisco A.Cortina – “D’artiste: Character Modeling” – Ballistic Publishing 2005.
Many people use image plane with eye lashes texture on it. But this will make the eye lash look flat, and not good enough in close-up shot. I do some extra study of different method in making eye lashes. Some people use Hair & fur in Maya or Hair plugin to make this, but it’s still not really food for close-up. I find out that the best way to do eye lashes is: polygon eye lashes! Despite of what method we use but the output should be polygon. Polygon eye lashes have a better look with more depth feeling and cast nicer shadows.
We can use Maya paintFX or third party- plugin to make the eye slashes then convert it to polygon. I find myself comfortable with the method of using Maya paintFX hair to model eye lashes then convert it to polygon, this way I can still render the eyelash properly in polygon form while keeping the construct history of PaintFX, I can modify the randomness, the thickness as well as the number of strands).
5.4- Nose & lips
“Both nose and lips contain some of the most subtle variations in shape on the faces. As with drawing and sculpting faces, the key is understanding the planes and angles they flow based one the underlying bones and muscles.”
Francisco A. Cortina -“D’artiste: Character Modeling” – Ballistic Publishing 2005.
Through researching, I found some good topology layout for those areas:
The edge around nose area form a round curve starts from top of the nose and go along ala and terminate at area where Philtrum meet nostrils. The mistake we often have is that edge loop doesn’t go around the nose but grid-like edge loop instead, it make the nose look square and big.
In the lips area, we should have at least 2 edge loops go out at the lip’s corner or else the model’s mouth look like being cut. Also, to emphasize the shape of the lips, we should add an extra edge loop around lips areas because without this edge loop when we smooth or subdivide one more level, the lib shape will be smoothed out.
In addition we model the head with close mouth but it’s better to have some extra face loop inside the mouse just in case to hide the border edge when character open his mouth.
At the chin area we should terminate edge that run from above with a square polygons area. This topology will make we adjust the shape of the chin easier or just in case when our character have a double chin. We should also have an edge loop start from chin and terminate at ear, this will form our character’s jaw bone more nicely.
Ear is a very tricky area in the face, it has spiral structure with a lot of detail in, if we are not careful we might end up spending too many polygon for it. The easiest way is to model the ear separately while keep in mind that its edge flow need to meet with the head topology, in the end we can sew the ear to the head model, we may have some triangle around the sew area but they are hardly ever deform while animation so it is totally safe. This separated ear model can be reused for any other models in the future.
It is essential to keep in mind that whether our model are good enough to move on to other stage like UV or sculpting. We should always review our topology one more time before continue moving to next step to check for unnecessary edge loop, triangles, badly deformed face etc. This will make our work much easier later.
– UV mapping:
It is necessary to keep the topology of the model as symmetrical as possible unless we have to model character with half of his face altered. This will help us a lot in UV and texturing whether we do it in Maya or other software.
– Animation check lists:
– Review our topology to check whether our character’s face will have a good deform when doing expression or not.
– If our character will talk or open his mouth, we will have to hide the open edge of the inside lips area or we have to model the mouth’s inner interior.
– Putting extra edge loop in the upper eye lids area so we will have enough polygon for the eyelid to cover the eye ball when character closes his eyes.
– Just in case that the character might have frowning or glaring expression, the forehead area will form some wrinkles here. Unless if we want to do it by texturing, we should add some extra edge loop around fore head area so that we can have enough polygon to make those wrinkles deformations. But this is not always necessary if we don’t want such realistic deform.
Modeling human face is a common topic in 3D graphic. It can be said that face modeling is a simple task, but the most difficult things lie in the harmony of details and shape that make up the unique characteristic and natural of the face. A small change can lead to a vast difference, sometimes it’s difficult to evaluate whether the face look right or wrong, if it looks wrong, which part should be edited? A realistic and successful face model will depend much on texture, shader and lighting, however these parts can never be success if they don’t have a solid steady base – the model itself.