Physiologists who hacked a digital camera for their lab work are now seeing the homebrew modification turned into a technology that could squeeze high-speed video out of consumer cameras.
and 鈥榮 team at the University of Oxford wanted to record rat heart cells in action, so they trained two cameras on tissue samples in their lab. A high-speed movie camera filmed the cell鈥檚 pulsing activity , while a normal stills camera captured detailed images. But aligning the two sets of images proved fiddly and frustrating.
So the team took an off-the-shelf video camera to pieces and rebuilt it to perform both roles, simultaneously recording high-speed video and high-resolution stills.
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Micro mirrors
They achieved the trick using a component most common in another consumer gadget 鈥� a home cinema projector. These projectors contain a digital chip studded with tiny, moving mirrors, each of which controls the brightness of a pixel in the projected image.
The Oxford team fixed one of these chips between their camera鈥檚 lens and its image sensor. They used the chip鈥檚 mirrors as a selective shutter, chopping up every frame of video captured by the camera into 16聽lower-resolution frames. In this way, they were able to squeeze 400聽frames per second out of the 25聽frames per second the camera was designed to record.
The chip does this by ensuring that only one-sixteenth of the sensor鈥檚 pixels receive light at any moment. It divides the image into squares four pixels across. Then, within each standard camera frame, the chip鈥檚 mirrors direct light first onto only the first pixel in each square, then the second, third and so on.
This means that each frame in the image is only one-sixteenth of the camera鈥檚 full resolution 鈥� 62,500 pixels instead of 1聽megapixel. But Bub says research-grade high-speed detectors costing 拢60,000 typically have comparably few pixels. 鈥淎nd the mirror array can be bought for a few hundred pounds.鈥�
By using an array with even more mirrors it鈥檚 possible to boost the frame rate even further 鈥� albeit with further losses in resolution. The team鈥檚 latest setup can capture high-speed movies at over 6000 frames per second.
Sharper images
But the footage from the modified camera is more useful than that from a high-speed camera. Because each set of 16 sequential frames come from different pixels on the same sensor, they can be combined to yield the same higher-resolution images that an unmodified camera would produce.
Silicon chip engineer Mark Pitter at the University of Nottingham, UK, was impressed with an early presentation of the Oxford team鈥檚 work. He has devised, and will shortly patent, a silicon chip to perform the same role as the mirror array but more reliably and at lower cost.
This more refined version of the original model could see the 鈥渕ovie鈥� and 鈥減icture鈥� settings on consumer digital cameras combined, says Bub. 鈥淵ou could later turn a series of high-resolution images into a movie, or decode a movie to produce a high-resolution still,鈥� he says.
Journal reference: , DOI: 10.1038/nmeth.1429
