7 top motion capture tips

Rebecca-Louise Leybourne shares her tips on the most overlooked, but vital parts of the mocap pipeline.

Motion capture top tips

Motion-capture technology has become a regular fixture in today's games, visual effects and film industries. The development and production of state-of-the-art systems over the last decade has enabled the creation of photoreal, computer-generated characters complete with realistic emotions and movements, that have been brought to life by capturing a human actor's performance.

But while we celebrate and admire the end result of characters such as Gollum from The Lord of the Rings trilogy or the Na'vi from Avatar, the creation of each of these digital creatures would not have been possible without a journey through a pipeline of several stages, each one as vitally important as the next to achieve the high-quality result required.

Data reconstruction and tracking is the often-overlooked first task in the performance-capture post-production pipeline - and as such, it is an essential to get this part of the process right first time, in order to avoid any time-disturbing repercussions further along the line.

01. Marker labelling

Labels define what role each marker plays in the skeleton of the human body

A character skeleton (VSK) is created from the range of movement, performed on the day of capture, using the marker layout positioned on the actor to predict the bones' length and rotation. This is then calibrated to create a labelling skeleton (VSS), which is used to define what each marker is.

02. Quality control

While many steps of the process can be automated, playing back the movement in half speed and trusting your eyes to check for noise movements or swaps is always useful. Also, it's a good idea to pass the file on to someone else for a fresh look before exporting the file.

03. Data swap

Where markers are in close proximity, such as the hands touching together, the resulting data can get confused

Swaps in data are often caused by using an automated labelling tool or sometimes, if the markers come into close proximity to each other, such as inner knees touching, the skeleton can get confused.

04. Graph editor

The graph editor should be familiar as it’s similar to graph editors in other 3D software

The graph editor should be familiar as it's similar to graph editors in other 3D software. It shows the keys and movement of individual markers.

05. Cleaning the noise

Cutting keys to remove noise requires thought, care and precision

Noise is fairly common on the hands and feet. When cutting the keys to remove noise, the gap made must be filled by taking influence from other noise-free markers surrounding the problem marker. If a file is particularly noisy throughout the entire movement, filters can be added to improve the data, but these can dampen the movement if used too excessively.

06. Character management

Character management allows you to control which skeletons can be viewed or edited in a file

Character management allows you to control which skeletons can be viewed or edited in a file. This can mean working on one priority skeleton then exporting them separately once completed to speed up the delivery time to the next part of the pipeline, as well as enabling multiple people to work on one file.

07. Unlabelled markers

Each marker in a marker set is named into relevance to where it is on the body

Each marker in a marker set is named into relevance to where it is on the body and then split into left and right. When a marker is blue is it unlabelled and requires manually connecting to the correct label. Here the RTHM3 is red in the list highlighting that there is no marker currently connected to this label.

Words: Rebecca-Louise Leybourne

Rebecca-Louise Leybourne is a motion-capture tracker at The Imaginarium. On stage she runs real-time and head-mounted cameras. This article originally appeared in 3D World issue 180.