June 25, 2024


Art Is Experience

3D Character Animation – Introduction to Motion Capture and Free-form Animation in 3D Max & Maya

A popular (yet often expensive) way to animate 3D characters is by using motion capture hardware. Motion capture dates back as early as 1915 when it was invented by Max Fleischer, involving only the use of cameras and drawings. In its earliest stages it was the study and capture of human and animal locomotion, known as rotoscoping. This information was used to aid artists in animating cartoons, such as “Koko the Clown” and “Snow White”. The pioneer of turning this work into entertainment was Walt Disney, which was without a doubt the most successful and well known 2D entertainer.

It is now used to digitally capture human movements using specialised hardware, often in the form of a motion capture suit worn by the individual. These suits vary in complexity and cost, the more advanced suits often require less post-processing such as cleaning of the data. There are four types of motion capture systems. The first is inertial motion capture systems, which utilise a number of tiny sensors to track the motion of joints and limbs. This data is then sent wirelessly to the host computer, which requires no external tracking hardware such as cameras etc. These suits are in the £25,000 range (Wiki 2008).

Mechanical motion capture systems come in the form of a set of semi-rigid plastic rods, containing a number of potentiometers that measure the movement and angle of the joints. The suit is worn like an exoskeleton, with the control box located on the waist or back of the user. The advantages of this system are that its occlusion free and low cost from £12,500 (Wiki 2008), making it a popular choice for small studios and educational institutes.

Magnetic systems use a series of coils through the suit that measure changes in voltage and current, to determine position and orientation of parts of the suit. The advantage of this is similar to the mechanical systems, in that they are not subject to occlusion or interference from reflective surfaces. However, they are vulnerable to EM and electrical interference.

The most modern and by far advanced motion tracking system is Organic Motions Markerless Motion Capture System (MMC), that was featured at the Consumer Electronics Show 2008. Subjects do not need to wear a suit or any kind of marker system. Instead, the system uses complex algorithms to identify and make sense of human movement, detecting which part of the body is what. However, it has trouble detecting subtle movements of certain areas, such as the fingers and facial expressions as reported by Wiki (2008) “These systems work well with large motions, but tend to have difficulties with fingers, faces, wrist rotations and small motions.”. As the external tracking system technology improves, it will no doubt be able to capture every motion and expression efficiently.

Similarly to traditional 2D animation, 3D animation can be created by hand. This is the cheapest and slowest way to animate a character in 3D. Likewise, in order to create a realistic animation, the artist must have a good understanding of human/animal movement. It involves incorporating physics and emotion into these movements, such as the characters weight and personality. Both of which will effect how the character moves, even in a basic walk. A crucial part of making this happen, is to create good joints.

This is done by making sure the weight gradient between the bones is a smooth curve, e.g. a bias of 33% / 50% / 66% to bone A. This is opposed to a straight gradient such as 25% / 50% / 75% which creates a hard deformation, whereas a curved gradient results in much smoother deformation. Most importantly is to add a ring of vertices that are effected by both bones. Allowing these bones to deform the far parts of the mesh, your creature or person will animate much better. This method should be applied to any joint. The crimping that occurs due to the nature of 3D joints can be corrected by using the Skin Morph modifier (in 3D Max). Much sharper bends can be achieved using a 12.375% / 33% / 50% / 66% / 87.6% gradient bias to a bone. As more gradient values are added, it takes longer to setup the deformation with Skin Morph. This method of gradient falloff can be applied to any character rigging tool within the myriad of 3D applications available.

In my next article I will lead you through the process of creating a very simple joint in 3D Max.