Inside the Camera: Traditional CCD or Tomorrow's CMOS Chip?

While our industry has installed many a camera, often not much thought at the dealer level is given to the actual guts of the camera. The focus is always on whether the camera can give you the images that the user requires, and often what price that will cost, and how simple it is to install and maintain.

However, there is a slight movement in our industry, at least among manufacturers, that is wrestling over the guts inside that camera. On many a camera's spec sheet, you'll notice a line about the sensor. It's either a CCD or CMOS, the two standard technologies used to capture light in such a way that it represents as close as possible to what the eye would see.

In the world of professional security cameras, the CCD has been the standard. The CCD, or charge coupled device, is basically a small chip that is sensitive to light. This silicon chip essentially receives light and turns it into voltage variations -- the data of an image. It's usually measured in inches -- the 1/3" CCD is the standard imager you'll find in video cameras used for professional security, but it's by no means the only one. Other sizes include 1/4", 1/3", 1/2" and even 2/3". In higher-end broadcast cameras, larger CCDs have been used and some of these high-fidelity manufacturers have even used three CCDs to expertly capture the image.

On the other side of the court is the CMOS chip, which was actually developed slightly before the CCD (both technologies were first developed in the 1960s and pushed forward by companies like Fairchild Semiconductor and RCA). CMOS stands for complementary metal oxide substrate, and at it's core, it does the same thing a CCD sensor does. It absorbs light and converts that into data. Like CCDs, CMOS chips are measured and usually size in inch measures, with 1/4" and 1/3" as the most common. The interesting thing about the CMOS chips it that they don't have to be used exclusively for imaging. They basically are memory chips, and are used that way in many devices, including personal computers.

OK, you say, what's so important about all this?

The key to keep in mind is that the CCD has been the standard for video cameras for a long time. If you've got a stack of old camera spec sheets, we'll venture to bet that you can find the CCD listed as the sensor on even your fairly old cameras, while you'd be highly unlikely to find a CMOS chip listed.

That just might be changing.

A variety of manufacturers, including Micron, Pixim and OmniVision, made a splash at the ISC West show in Las Vegas as they unveiled a variety of CMOS imagers designed specifically for surveillance cameras. CMOS chips are no stranger to surveillance cameras. Products from established companies like GE Security, Axis Communications, EverFocus and others have used CMOS chips in some of their cameras, but by and large, manufacturers have stayed transfixed on CCDs.

It's actually a tad surprising, since CMOS chips have had such a price lead on CCDs. The CCD has tended to add a cost of around $10 per camera; CMOS sensors, on the other hand, have been able to be produced for well less than $10 per sensor. But that slight price difference hasn't been enough to yet overthrow the CCTV market, where much of the cost still lies in the cabling and installation that support a surveillance camera.

And while many suspected that the cost issue would eventually override the CCD based purely on price point, even as CMOS chips were able to be manufactured less expensively, so were CCDs able to drop in price. And even though they couldn't quite keep up with the price drops that CMOS manufacturers could offer, that ability to chase them in prices has helped ensure the CCD's longevity in surveillance cameras.

There's also an issue of quality in many manufacturers eyes. CCD sensors have, most would agree, stayed a slight step ahead of CMOS sensors in terms of versatility.

"It's getting better, and it's getting very close in quality," said Fredrik Nilsson, general manager for network camera manufacturer Axis Communications. "For indoors, CMOS is really as good [as CCD technology], but for outdoors it's not as good because it's not as light sensitive."

The CCD chips, note Nilsson, are so sensitive to light that they are excellent for low-light situations. That ultra sensitivity even requires that the cameras use auto-irises so that too much light isn't fed onto the CCD chips, which could cause streaking in the image.

The CMOS chip of 2006, however, isn't the CMOS chip of old. The old chips were notorious for lacking light sensitivity and for having resolution problems of "noise" on the chip. Today's chips may not have quite the light sensitivity of CCDs, but some manufacturers, such as Pixim's new chips, are able to capture color images at light levels down to 0.5 lux. Along the way, the signal-to-noise ration dropped as well, offering less noisy images, and the width of the dynamic range increased.

But even as they improved, the CMOS chips still primarily found their way into low-end still cameras and started to take over the camera-phone market.

Part of the reason is not only the cost, but the size. CMOS chips actually are able to receive the light and convert that into the data right on one chip. The "logic" is actually embedded in the silica. A CCD, on the other hand, actually converts the light into analog electrical variation, and then needs a second analog-to-digital (A/D) converter chip to "flip" that data back to digital if it's going to be used in an IP-camera. However, that analog functionality was a featured that solidified the CCD's position in video surveillance, when the market was almost exclusively analog cameras. Because it requires that extra conversion chip, CCD cameras will always be slightly larger than cameras that solely use CMOS sensors.

That's allowed CMOS to hit the market of smaller cameras, according to Micron's Director of Market Development Paul Gallagher. The low cost, adds Gallagher, has also enabled CMOS chip manufacturers to help drop the cost on lower-end cameras, such as those used for residential surveillance, and has had a similar effect in thermal imaging cameras as well. Now, says Gallagher, the CMOS chips are showing up in very high-resolution cameras -- the so-called "multi-megapixel" cameras, and even the high-resolution fisheye style cameras that allow users to operate with a digital pan, tilt and zoom, moving through the field of view with full resolution without ever having to mechanically change the camera's position.

So for now, where does that leave us?

Here's a quick summary:

CCD: Higher-priced, but great for cameras that may require vision in near darkness. The lack of noise has helped solidify this camera technology's market share lead, and with big manufacturers like Sony producing the CCDs, they have huge staying power. They still offer a slight advantage in image quality over CMOS chips, and your buyers are likely rather familiar with this tried-and-true technology.

CMOS: Lower prices and improving quality. Great for fixed-light environments, and the lower cost will help these chips take off in cameras used for residential installations and lower-end commercial facilities, especially for cameras used to verify intrusion alarms. The size makes them attractive for compact cameras, and the direct-to-digital format will likely seize upon the growing network camera market.

Finally, we asked Axis' Nilsson, how he expects to see the market share between the two sensors change. He says his company is already using CMOS sensors in some of its cameras, but still heavily relies upon CCD sensors. He adds that while he knows the change is coming, but he's not so sure that there will be a rapid change from CCD to CMOS.

"In 1999, we said it would take two years before CMOS started to be prevalent in the professional surveillance market," said Nilsson. "Now, in 2006, we still say two years. It's estimated that 95 percent of surveillance cameras are still CCD cameras, so there is a big market that has to change."