CCD or CMOS for your digital cameras

The small size of some cameras on the market is astounding. Look at the camera on your cell phone, it is even smaller than the tip of a pencil. Some models have camera units that can be rotated 180 degrees to allow you to take your own picture.

Whether it is part of your cell phone, or a high-end, professional SLR camera, at the heart of every digital camera is an image sensor. This sensor has components that are photo- sensitive, and the light is converted into electrons. A microchip then converts the analog data into digital, which is then processed again to create a representation of what the sensor "sees" through the camera's lens.

The image files may then be compressed using the standard that the camera uses. You usually have the option to keep the files uncompressed using the camera's proprietary standard. Canon digital cameras, for example, use a native format that the company calls RAW. Such an uncompressed format will allow you to manipulate the images with the best results, as no picture elements have been lost.

Types of sensor.

Generally, two types of sensors are used in today's digital cameras: Charge-Coupled Device (CD) and Complementary Metal-Oxide Semiconductor (CMOS).

The CCD is commonly used in scanners. It generally produces high-quality pixels because of, among other things, its higher sensitivity to light. It is more reliable, too.

The downside is that it is bulkier and more expensive to make compared to the CMOS. The CMOS has another advantage over CCD, it consumes less power -- up to 100 times less -- and, therefore, is more suitable for battery-powered handheld devices, such as handheld scanners, cell phones, PDAs and notebook cameras.

Because of these benefits, R&D in CMOS has been quite active in the past few years and can be expected to accelerate in the future. Companies actively developing CMOS-based image sensor include the chip-maker Micron.

Unlike the CCD, which requires a special manufacturing facility, the CMOS image sensor is cheaper to produce because it can be made in a standard manufacturing facility for microchip.

One of the problems with CMOS is its susceptibility to noise, which the CCD is more immune to. The noise can be color infidelity, especially in the peripheral areas. However, as you probably know, Canon believes the noise problem can be addressed and the company has, in fact, decided to use CMOS in their SLR cameras, starting with Canon EOS 1D Mark II.

Actually, the noise can be eliminated to a large extent using a noise-suppressor circuitry and other techniques such as double- sampling. The CMOS can also be integrated with the chip, and this enables the integration of various camera functions in a very small package.

Even midrange cell phones now come with an integrated digital camera. The high-end cameras usually have video capture capability. This means that the development of high-quality CMOS- based image sensors will continue to make progress. There will be other applications that will drive the R&D work.

Keep in mind that more and more cars are now equipped with cameras on the sides and in the rear to make driving safer. Cameras are also used to determine the size of the driver or passenger so that air bags can be deployed in the right size for their body size, to maximize their effectiveness.

For the time being, most stand-alone, high-resolution digital cameras will still be using the CCD, while cameras embedded in cell phones will use CMOS to keep their sizes down and their battery consumption to a minimum. However, in the future, the CMOS may well overtake the CCD. --- Zatni Arbi

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