The idea of a single-pixel camera may sound downright weird. But Richard Baraniuk, an electrical and computer engineering professor at Rice University, claims that a camera that captures several thousand points of light in rapid succession makes more sense, and is far more efficient, than one that simultaneously grabs several million pixels.
We can take a picture with potentially millions of pixels, but using just
a single detector element, he says.
Baraniuk and Kevin Kelly, a Rice assistant professor of electrical and computer engineering, have designed a camera that uses a digital micromirror device (DMD) developed by Texas Instruments. The DMD takes the place of the charge-coupled device (CCD) or CMOS array found in conventional digital cameras.
Used primarily in digital televisions and video projectors, DMDs are chips
covered with thousands of tiny, microbe-sized mirrors. Each mirror can face
in only two directions, appearing alternately dark and bright, registering its
current state as a 1 or 0. The new camera focuses light through a lens onto
the DMD (). A second
lens then collects the light reflected from the mirrors and focuses it onto
a single photodiode sensor.
This is the single pixel that takes our measurements, Baraniuk says. Each
time the DMD mirrors shift, the photodiode records a new pixel value. Baraniuk
maintains that pixel overkill burdens most conventional cameras.
Even though your picture consists of 5 million pixel values, most photographs
can be described [via compression technology] using a lot fewer numbers, he
says. At a 100:1 compression ratio, for instance, just 50,000 values would be
needed to approximate a picture. You've built these 5 million detectors only
to throw away most of the numbers they produced in your compression system.
The new technology promises to eventually lead to cameras that rely less on
expensive hardware, such as powerful microprocessors, CCDs, and memory devices,
and are therefore cheaper and more power thrifty. The JPEG number crunching
drains your camera s battery power, Baraniuk says.
But there's one not-so-slight drawback to the technology: The prototype model
requires about five minutes to take a single picture. That s because the camera
must blink several thousand times to capture a complete image. We re not claiming
we'll replace conventional cameras tomorrow, Baraniuk admits.
Yet Baraniuk notes that the camera already is well suited for some imaging
applications at wavelengths outside the visible spectrum tasks that would bust
budgets using conventional CCD and CMOS imaging arrays. For example, a 1-Mpixel
camera comprised of detectors that each cost $1000 would cost $1 billion, while
our setup would cost just over $1000, he says.