Computational rephotography is a fancy name for photos taken from the exact same viewpoint as an old photograph. Actually, that's just rephotography. The "computational" part is when software helps out.

I'm a sucker for photos of old street scenes. Seeing familiar parts of your city as they were many decades ago is fascinating, and if people are good enough to snap a new version, you can enjoy the differences of places you have never seen. At Flickr and a site called Historypin, you can see the old shots lined up over the new, like a window into the past.

Researchers at MIT have found a way to automate the process. Currently, they use a laptop to do the heavy lifting, but the software could just as easily sit inside a camera. In fact, that's the plan. The system compares the scene in front of the camera with a historical photograph. It then works out the difference between the two and gives the photographer instructions along the lines of "up a bit, left a bit more."

According to an abstract on rephotography, it is a lot more complicated than it seems. In lining up the images you must consider "six degrees of freedom of 3-D translation and rotation, and the confounding similarity between the effects of camera zoom and dolly."

Gimmick? Sure, but then so are all manner of the features in the modern digicam, from smile-detection to facial-recognition to fancy sepia modes. Today's camera is essentially a computer with a sensor and a lens, so why not pack in everything you can? And if it means getting to see more old-time streets scenes, I'm totally in.

Camera app puts you in the footsteps of history [New Scientist via Alex Madrigal]

Computational rephotography [ACM]

Photo: Nomad Tales/Flickr

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