For those of you who are less familiar with this aspect of content origination, motion or performance capture is the term most commonly used to describe the digital capture of movement of an object or person.
The most common forms of modern motion capture systems
- Magnetic – The performer wears sensors at key points of the body that measure signals from a low-frequency magnetic source in order to track movement. This can sometimes be disrupted by interference from the surrounding environment.
- Mechanical – The performer wears an exoskeleton that tracks their movement. This method can be cumbersome so isn’t used as often.
- Optical – The performer wears a suit with ball-shaped markers or LED lights marking different points of the body. Anywhere from 16 to over 100 cameras capture the movement and use infrared light to track these reflective markers.
- Inertial – Special sensors on the performer take measurements to record their own movement, which can be combined to show overall movement.
But motion capture is by no means a new technique
In 1878, using 24 cameras lined up 12 inches apart, British-born photographer Eadweard Muybridge created The Horse in Motion, a series of sequential photographs that proved that all four feet leave the ground when it runs.
Muybridge, under the auspices of the University of Pennsylvania., then went on to produce a more in-depth study of the subject – Animal Locomotion: An Electro-photographic Investigation of Consecutive Phases of Animal Movements, A more controversial study of the relative ways that women and men moved followed that drew heavily on gender stereotypes for its research and findings.
Then, in the 1898s, Muybridge got involved in something that will look a bit more familiar
This is a letter from one of his collaborators to another …
Eakins, Godley and I were out there yesterday trying a machine Eakins had made […]. We sewed some bright balls on Godley and ran him down the track. The result was not very good although you could see the position of the buttons at every part of the step. But afterwards Muybridge took him with his machine and got a very good result even showing his black cloth.
Thomas Anschutz
Meanwhile, in France …
Around the same time, and completely independently of the work being doing in Pennsylvania, French scientist and physiologist Étienne-Jules Marey combined photography and time to create what he called ‘chronophotography’. He developed a photographic gun that took 12 photographs a second from a fixed point.
The technique was much more accurate than Muybridge’s. The images were taken on top of each other on a single photographic plate, which showed the path of movement more clearly to the human eye, though it couldn’t clearly show slower sequences of movement.
Marey’s big insight, however, was to create stick figures / skeletons using shiny buttons for joints and connecting metal bands. Now, up to 100 photographs per second could be taken without movement being obscured.
Frank and Lillian Gilbreth’s Chronocyclegraphs
In the early part of the Twentieth century, the Gilbreths specialised in industrial engineering and operational efficiency. Their “chronocyclegraphs” involved attaching small incandescent bulbs to workers’ fingers and taking long exposure photographs of of them performing their tasks.
Later, echoing the Gilbreth’s work, Preston Blair’s 1946 animation reference guide, ‘Advanced Animation’ added a ‘line of action’ to show the rough direction of movement of characters over time.
Rotoscoping
Again, for those not familiar with the term, rotoscoping, which was pioneered by brothers Max and Dave Fliescher in the 1910s, was, early on, a process whereby motion was captured frame-by-frame and projected onto a glass sheet so the live subjects could be traced, translating real-life movement directly into animation. One of their early attempts, shown above, features a rotoscoped Dave wearing a clown suit.
As with the Gilbreths and their industrial research, it was all about making cel animation more efficient, especially with the advent of colour, though purists argued that it was cheating.
Modern motion capture
Today, while skin-tight suits and markers still predominate, companies like Move AI are offering machine learning-based markerless system that serve to push the boundaries even further.
What’s next on the horizon?
At Mondatum we have many years experience in the science, technology and techniques used in motion and performance capture in all its forms.
If you would like advice, guidance or support for your next mocap production, please get in touch with Colin Birch (colin@mondatum.com) or John Rowe (john@mondatum.com).
Source: Science & Media Museum