Pixim Boosts Dynamic Range for Digital Video
EXTREME TECH
Pixim Boosts Dynamic Range for Digital Video
February 18, 2003
By: Bill Machrone
What you see isn't what you get, at least not with digital
video. The big problem with the typical CCD image sensor is that it
can't do what your eye does - adjust automatically and continuously to
varying levels of light. When you look at a scene that contains both
light and dark areas, your eyes reduce their sensitivity to bright
areas and increase their sensitivity to see dim objects and details in
the shadows.
A CCD sensor can adjust to bright and dark scenes, but not
simultaneously. So when you're panning around the room with your
camcorder, the exposure is fine. But if a sunny window appears in your
frame, it's washed out; you can't see anything outside. Conversely, a
bright object in the foreground swamps dim objects in the background.
Everything in the shadows fades to black.
A limited brightness range doesn't adversely affect your home videos,
and is often used as an artistic effect in film. But it's bad news to
the security camera market. If the bad guy is in the shadows, you can't
identify him. If detail is lost in an overlit scene, valuable clues may
be missed.
Pixim addresses this problem with a new CMOS sensor technology, Digital
Pixel System. DPS processes the image on a pixel-by-pixel basis. Items
in the shadows are clearly visible, despite bright foregrounds.
Intensely lit areas don't wash out. Pixim's split-screen demonstrations
were dramatic and convincing, and they've convinced the security camera
industry, with five of the top vendors lining up to be Pixim customers
- and more on the way.
In the first photo, you can see the Pixim image sensor assembly on the
left and a typical Sony CCD assembly on the right. The CCD system is
larger and more expensive because it's an analog technology, and uses
roughly three times as many components. The Pixim system, by contrast,
is digital, with companion chips that sense the image and process it on
a pixel-by-pixel basis. The onboard ARM-100 processor gives the camera
builder a choice of PAL or NTSC output and dynamically adjustable
sensitivity.
We snapped a photo from a CRT that was showing output from a CCD camera and a Pixim camera side by side. As you can see, the Pixim shows objects outside the door clearly, and indeed, our digital photograph doesn't do justice to the actual display on the screen.
Although the resolution and contrast needs are different in the security space, it's likely that this technology will ultimately benefit consumers as future versions find their way into digital cameras and camcorders.
