Tuesday, June 9, 2009

Mocap Ain't Just for the Movies!

There is a common misconception that motion capture is an invention of the movie industry. In truth motion capture for movies only began in the late 1970's. Before this, motion capture was used primarily to analyze both animal and human motion and sports performances. There is some fantastic footage from the early days of motion capture and we will share some of that video and its history with you.

The first recorded video analysis was performed by a photographer, Eadweard Muybridge in 1878. For this video analysis Muybridge was asked by the then Governor of California, Leland Stanford, to settle a debate. The debate concerned Stanford's belief that all 4 hooves of a race horse leave the ground at the same time when the horse is galloping. Muybridge used 12 cameras set up along a race track. The cameras captured images at 1/1000 of a second. This is not the same as a video camera capturing 1000 frames per second but we can still appreciate that the cameras were capturing motion at high speed.

Muybridge was a professional photographer and understood enough about motion capture to set up his cameras in the correct position so that he could see whether all 4 of the horses legs came off the ground. He also understood the need for capturing the images at high speed (1000 frames per second) because of the speed at which the horses legs move. If you would like to find out more about camera setup and camera specs that will result in excellent video analysis, check out Video Analysis of Sports 101 and Sports Analysis: The Camera Specs .

Below is movie made from the sequence of photographs taken by Muybridge with his 12 cameras. You will see that the cameras were positioned on the one side of the horse and he covered the background with a white sheet to make it easier to analyze the photographs.

Muybridge was commissioned to prove Governor Stanford's argument and he did that showing that all 4 hooves of the horse do come off the ground simultaneously when galloping. Here is a still shot of the horse in the air. You can see this plainly in frame 3 below.

Muybridge did not stop there and went on to analyse all types of motion. He studied numerous sports including baseball pitching and hitting, tennis serving and javelin throwing. Muybridge preferred his human subjects to be naked when he captured images of them for analysis. He felt that in order to properly analyse the motion he needed to be able to see the body unobstructed by clothes. In this he has a point, as it is can be difficult to accurately analyze motion when the joints we are interested in are obscured by clothing. We are not suggesting you do your motion captures naked. Luckily, these days sports clothing is a lot more form fitting than back in the 1870's and the problem of loose fitting pants obscuring our view is less likely.

If you are interested in finding more of Muybridges photographs, you will find many online. Just remember we warned you that some may show naked subjects.

Please leave us a comment and let us know what you think. If you have any suggestions about what you would like us to see analyzed let us know.

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