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A computer system that recognises dance moves could synchronise music and lighting with a performance, or be incorporated into an interactive computer game, its designers say.

Researchers at Arizona State University in the US developed the system, which can recognise dance moves from normal video footage. They previously created a system that tracks a dancer’s movements using markers attached to their limbs and joints – a motion analysis technique known as “motion capture”.

“Using normal video cameras will make interactive dance performances user-friendly,” says Gang Qian, a member of the research team. “It’s less intrusive because there is no need to put markers on the subjects, and conditions like lighting and costume can be more flexible.”

The researchers worked with professional dancers to develop the system, which uses two video cameras, one behind a dancer and the other to one side. “With two cameras, the system can identify dance poses more accurately,” Qian explains. “There are many ambiguous poses when using only one camera.”

Dancing shadow

Video footage of a performer is fed to a computer that removes the background to produce a pair of white-on-black silhouettes. The computer then converts these silhouettes into numerical coordinates that can be compared to a library of twenty modern dance poses already stored in the system.

If the computer finds a statistically close match it signals that it has spotted a particular dance move. In tests involving different dancers the system was 83% accurate at identifying the moves stored in its memory. This could allow it to synchronise background music or stage lighting to an improvised dance performance, the researchers suggest. Or it could be incorporated into a dance-based computer game.

But Sean Gong, who researches computer recognition of human behaviour at Queen Mary’s University in London, US, says the system could also have limitations. “One of the problems with silhouette-based recognition is that it is very view dependent,” he told Â鶹´«Ã½. “You would need to have no clutter around, a relatively clean background, and the same viewing angle for the [computer] training and the final performance.”

Gong adds that dancers probably need to be disciplined to ensure particular moves are recognised. “But dancing is probably one of the most challenging human movements to track,” he adds, “and perfecting these systems could lead to the development of new kinds of entertainment.”