New device takes photos with a flat, 'fully transparent' polymer sheet
An Austrian research team has announced a new way of capturing images on a flat, transparent polymer sheet.
The device looks like something out of a dystopian future and is being touted by its developer as the first "image sensor that is fully transparent – no integrated microstructures, such as circuits – and is flexible and scalable at the same time.”
The sensor consists of a polymer known as a luminescent concentrator—the material absorbs a specific wavelength of light and re-emits it at a longer wavelength.
The outer edge of the polymer film has a series of optical sensors that are similar to 1D pinhole cameras. These sensors capture light and send the information to a computer that can then create a grayscale image.
The new technology can also read movements and perhaps be used as a control system for a computer. Developers hope that the new technology can be used to create a touch-free, transparent user interface that could overlay on a television or display.
The resolution of the prototype is low — only 32x32 pixels — but researchers claim that they can increase the resolution by using more sensitive photodiodes and more sophisticated computing algorithms. Color imaging is also possible, by layering sensors that are sensitive to different colors of light on top of each other.
Researchers are also looking into using the screen as an overlay on top of a normal CCD sensor and send two exposures to the camera. The resulting image, they claim, would be able record two photos at different exposure simultaneously to create HDR.
The press release explains how the polymer sensor works:
For the luminescent concentrator to work as an imager, Bimber and his colleagues had to determine precisely where light was falling across the entire surface of the film. This was the major technical challenge because the polymer sheet cannot be divided into individual pixels like the CCD camera inside a smartphone. Instead, fluorescent light from all points across its surface travels to all the edge sensors. Calculating where each bit of light entered the imager would be like determining where along a subway line a passenger got on after the train reached its final destination and all the passengers exited at once.
The solution came from the phenomenon of light attenuation, or dimming, as it travels through the polymer. The longer it travels, the dimmer it becomes. So by measuring the relative brightness of light reaching the sensor array, it was possible to calculate where the light entered the film. This same principle has already been employed in an input device that tracks the location of a single laser point on a screen.
The researchers were able to scale up this basic principle by measuring how much light arrives from every direction at each position on the image sensor at the film’s edge. They could then reconstruct the image by using a technique similar to X-ray computed tomography, more commonly known as a CT scan.
“In CT technology, it’s impossible to reconstruct an image from a single measurement of X-ray attenuation along one scanning direction alone,” says Bimber. “With a multiple of these measurements taken at different positions and directions, however, this becomes possible. Our system works in the same way, but where CT uses X-rays, our technique uses visible light.”
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