The idea of motion capture, or motion tracking, is hardly a new concept. It’s used for everything from sports, gait analysis in clinical medicine and robotics, to bringing videogame characters to life.
But methods of recording movement have existed far before the ping-pong balls attached to skin-tight suits that we think of when picturing modern motion capture.
What is motion capture?
‘Motion capture’ is the term used to describe the digital capture of movement of an object or person, though more broadly it refers to any process of recording movement.
The most common forms of modern motion capture systems include:
- 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 how did we first begin transforming real movement into art?
In 1878, British-born photographer Eadweard Muybridge published The Horse in Motion, a series of six cabinet cards, each containing sequential photographs that show a galloping horse. Commissioned by Leland Stanford, an American railroad tycoon who also bred racehorses, this initial study would later prompt a much larger and influential body of work.
To capture subjects moving quickly, Muybridge used a setup of 24 cameras lined up in a row, each 12 inches apart. The horse broke thin threads as it ran which triggered the electromagnetic shutters of the cameras. Movement had never been captured in this way before, and the images confirmed the longstanding theory that all four of a horse’s feet leave the ground when it runs.
The success of this work meant that Muybridge sought and received funding from the University of Pennsylvania in order to photograph hundreds more studies in 1884 and 1885. The product of this was Animal Locomotion: An Electro-photographic Investigation of Consecutive Phases of Animal Movements, a revolutionary collection of scientific photographs published in 1887. Pictured again as sequential images, the variety of animals in motion, including some borrowed from Philadelphia Zoo, were vastly outnumbered by human studies.
He first took the photos as part of a scientific investigation of motion, not realising that he was producing a useful tool for artists as guides for depicting movement. Later additions suggest he did become aware of this, as the captured movements seem more choreographed than natural with the models posed aesthetically, inspired by postures found in artwork. Images from the collection are still widely used as references by artists and animators today.
Several of the male models in the study were from the University of Pennsylvania, which only admitted male students at the time, and there is a clear distinction between the way men and women were captured and described. Men were chosen for their athletic excellence and tended to be young and fit, described as ‘experts’ or ‘champions’, whereas women were described using their physical characteristics and marital status.
As well as describing women using characteristics that seem irrelevant to their movement, Muybridge’s choice in models also sets an unrealistic expectation of how men should look – suggesting that they should all be young and athletic.
These stereotypes seep into the activities the models are photographed doing. Men are photographed practicing sports such as wrestling or fencing, while women are left to play lawn tennis, dance, and generally partake in more ‘graceful’ activities.
The single-sex nature of higher education promoted a differential treatment of the models, resulting in the aestheticization of the male model and the theatricalization of the female model.
Janine A. Mileaf, Poses for the Camera: Eadweard Muybridge's Studies of the Human Figure (2002)
Explore some of Muybridge's images:
Muybridge and his contemporaries working in and around the university and art schools in Pennsylvania often collaborated on projects including photographic motion experiments. During the early 1880s, a group of them carried out an intriguing experiment involving a method that is eerily reminiscent of modern motion capture.
This experiment was described in letters from Thomas Anshutz to J Laurie Wallace:
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.
This sounds a lot like optical motion capture with its LED markers, except recorded using photography rather than cinematography, which wouldn’t be invented for several more years.
Étienne-Jules Marey’s chronophotographs
Another set of motion studies emerged independently around the same time, taken by French scientist and physiologist Étienne-Jules Marey. His interest in movement also led him to photography, and he coined the term ‘chronophotography’ (combining ‘time’ and ‘photography’) to describe it.
In 1882 Marey developed a photographic gun that let him take 12 photographs a second, enough to synthesize the motion of a subject on a phenakistoscope. This method was much more accurate than Muybridge’s, and its single camera generated images from a fixed point of view.
Marey preferred to use multiple exposures, meaning that all the images were taken on top of each other on a single photographic plate. Presented like this, the image shows the path of movement clearly to the human eye, whereas it’s harder to see the differences between Muybridge’s sequential photographs when they’re side-by-side.
One drawback to Marey’s method of taking sequential photographs at a fixed rate is that it doesn’t show slower sections of movement very clearly. For instance, if you were to take 12 frames a second but the subject barely moves, the result would be 12 very similar images superimposed on each other—which actually obscures the movement rather than showing its path.
Muybridge and Marey usually chose to shoot their models in white clothing on a black background, as the high contrast allowed them to photograph the movements as clearly as possible. To avoid blurry, busy images, Marey simplified the appearance of his models further by dressing them in black and marking out a ‘skeleton’ on them with shiny buttons for joints and connecting metal bands. This captured all the important movement, as only the dots and lines made an impression on the photographic plate.
Reducing the subject to a stick-figure-like outline meant that up to a hundred photographs a second could be taken without obscuring the movement. He also altered the camera’s rotating shutter, making every tenth window in the disk twice as wide so that every tenth imprint on the plate appeared twice as intense. A clever addition, this made it possible to visualise the time that different movements took.
Marey continued to experiment and improve his devices over the years, as photographic technology improved too. By the 1890s, he was working with a system which captured sequential images on transparent celluloid.
Considering the invention of photography was only at the beginning of the 19th century, it’s incredible to see Muybridge and Marey use it less than a century later in ways that are so similar to how we still approach motion capture. They were limited by the technology that existed at the time, but the concept of their methods holds fast through to the 21st century.
Both men's work had a significant role to play in the origins of cinematography and moving pictures.
The Gilbreth's chronocyclegraphs
Frank and Lillian Gilbreth were industrial engineers and efficiency experts who began conducting motion studies for companies in the early 1910s to improve the productivity of their workers—often those on factory production lines.
Their aim was to analyse workers’ actions; if the right hand was doing more than the left, distributing the tasks more equitably would improve the flow of movement. This might involve rearranging their workstation.
The Gilbreths referred to one of their methods as producing “chronocyclegraphs”, which involved taking long exposure photographs of workers performing their tasks. The workers had small incandescent bulbs attached to their fingers so that the final photograph would show the path of movement marked by the light. To show the duration of movement, they could use flashing bulbs which were recorded as dashed lines.
Like Muybridge’s photographic experiment, this idea brings to mind modern motion capture suits with their LEDs. Preston Blair’s 1946 animation reference guide, ‘Advanced Animation’, also echoes the Gilbreth’s work, showing the technique of adding a ‘line of action’ to show the rough direction of movement of characters over time.
Rotoscoping: Capturing movement for animation
At this point, we begin to cross over into the realm of animated film, beginning with Max Fleischer, who emigrated as a child with his family from Krakow to New York in 1887. His employment as a newspaper errand boy eventually led to his becoming a cartoonist, at which point the step across to animation seemed a natural progression.
Fleischer and his brother Dave developed the rotoscoping technique in his living room in 1915, a method he went on to patent in 1917. The Rotoscope displayed film frame-by-frame, projecting it onto a glass sheet so the live subjects could be traced, translating real-life movement directly into animation.
Their first animation using this technology featured a rotoscope version of Dave in a clown suit, a character which went on to become Koko the Clown in the ‘Out of the Inkwell’ series.
Like the Gilbreths and their industrial motion studies, the early process of animation was also about efficiency. Hand-drawn, cel-by-cel animation was labour intensive, so companies would often assemble a production line for each stage, especially with the development of colour film, which added more stages to the workload.
The ability to directly copy human motion by rotoscoping was a method that greatly sped up the animation process, but it experienced resistance at first as traditionalists argued that it was a form of cheating. Motion capture still suffers from a similar stigma today, as it provides a base of movement for animators to build on top of, something that might be seen to require less skill.
Motion capture exoskeletons
Even into the 1980s, with great progress in the world of animation, motion capture technology was still being adopted from other industries. Tom Calvert, a professor of Kinesiology and Computer Science, developed a medical motion capture system in 1983.
Used like a goniometer—a device used to measure an angle, or a joint's range of motion—the exoskeleton system used potentiometer sensors to accurately track patients’ movement and feed it into a computer animation system. This allowed for the comparison of data over time—for instance to track the progress of a patient recovering from surgery.
The exoskeleton design was quickly adopted by the animation industry and refined into a less cumbersome suit, and the method is still widely used as a low budget option.
Modern motion capture
Motion capture technology has since become commonplace in the videogame and film industry, from animating characters such as Jar Jar Binks and Gollum to full length films such as The Polar Express and Avatar.
Even animators working with more ‘traditional’ techniques can still be found acting out and recording movement to use as references during the animation process and help them to achieve realistic movement.
The industry continues to develop, and with modern advancements it’s even possible to capture motion using smartphone apps.
Both Eadweard Muybridge and Étienne-Jules Marey became interested in motion photography as a result of an interest in physiology and science; neither initially considered its value to art. It's interesting to see how this trend continued with the Gilbreths’ motion studies and the medical applications of motion capture exoskeletons. Hopefully we will continue to innovate in the realm where science and art cross over—who knows what we could create?
So the next time a blockbuster animated film comes out and you’re watching behind-the-scenes footage of actors in motion capture suits, just remember that bearded Victorian gentlemen were running around doing similar things back in the 1800s!