Communications of the ACM
Can We See the Arrow of Time?
A new algorithm can determine whether a video clip is playing backward or forward, with 80% accuracy.
Credit: Jose-Luis Olivares/MIT
Massachusetts Institute of Technology (MIT) researchers have developed a algorithm that can determine whether a given snippet of video is playing backward or forward with 80% accuracy. They say their research could lead to more realistic graphics in gaming and film by identifying subtle but intrinsic characteristics of visual experience.
"We're trying to understand the nature of the temporal signal," says MIT professor William Freeman.
The researchers designed three algorithms, all of which were trained on a set of short videos that had been identified in advance as running either forward or backward.
The most successful algorithm begins by dividing a frame of video into a grid of hundreds of thousands of squares. It then divides each of the squares into a smaller, four-by-four grid, and for each square in the smaller grid it determines the direction and distance that clusters of pixels move from one frame to the next. The algorithm then generates a "dictionary" of about 4,000 four-by-four grids, in which each square in a grid represents particular directions and degrees of motion. Finally, the algorithm searches through the labeled examples to determine whether particular combinations of "words" tend to indicate forward or backward motion.
From MIT News
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