http://news.bbc.co.uk/2/hi/technology/6263551.stm?ls

Tuesday, 16 January 2007, 14:49 GMT

Single-pixel camera takes on digital

Researchers in the US are developing a single-pixel camera to capture
high-quality images without the expense of traditional digital
photography.

Being developed by a lab at Rice University in Houston, Texas, the
single-pixel camera is designed to tackle what its developers see as the
"inefficiencies" of modern digital camera.

It currently resembles an old-fashioned pinhole camera and is the size
of a suitcase, but assistant professor of electrical engineering Kevin
Kelly told BBC World Service's Digital Planet programme that it is only
"the beginning of things."

"Hopefully it will get smaller," he said.

Inefficiencies

The camera was created, according to Dr Kelly and his colleague Richard
Baraniuk, because digital cameras are very wasteful. They require
expensive microprocessors and massive battery power to capture an image
- most of which will not be used in displaying the picture.

This is because the captured image is compressed, to a jpeg file for
example, to make the file size smaller and more convenient to store.

"What is so inefficient about this is that we acquire all these numbers
- for example 10 megapixels - only to throw away 80-90% when we do the
compression process," explained Dr Baraniuk.

Although a digital camera picture may contain many millions of pixels,
most photos can be described with far fewer because there is a lot of
redundant or duplicate information in an image. For example a picture of
a blank wall will have many pixels with the same colour and texture
information.

Dr Baraniuk said that this is where the single-pixel camera really has
an advantage.

"Instead of taking the light from an object through a lens and focusing
it on a pixel array, we actually reflect it off an array of mirrors," he
said.

This digital micromirror device, as it is known, consists of a million
or more tiny mirrors each the size of a bacterium.

"From that mirror array, we then focus the light through a second lens
on to one single photo-detector - a single pixel."

Random mirrors

As the light passes through the device, the millions of tiny mirrors are
turned on and off at random in rapid succession.

Complex mathematics then interprets the signals assembling a high
resolution image from the thousands of sequential single-pixel
snapshots.

"In the last couple of years, scientists and engineers have figured out
that from these randomised measurements, you can actually reconstruct an
image of the object that is sitting in front of the lens," said Dr
Kelly.

The camera is hooked up to a computer to display the captured image
which can take minutes to construct.

Although at the experimental stage at the moment, if the device ever
makes it to market it could make digital cameras more efficient and
dramatically improve battery life by doing away with the need to process
and compress each image.

Using a single light sensor also means that it can be swapped, for
example, for an ultra-violet sensor on a satellite, or infra-red for a
night-vision camera.

"Instead of using a million really expensive sensors, we can use one
really expensive sensor and still give you a million-pixel image," said
Dr Kelly.

/end