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Monday, June 22, 2009

Camera Image Sensor Comparison

By Joe Morphe

An outdoor security camera, like all cameras, uses an image sensor made up of many pixels which registers the amount of light and converts it to the corresponding number of electrons. The brighter the light, the more electrons are generated. There are two main technologies used for the camera's image sensor.

These two types are the charge-coupled device, or CCD, and the complementary metal-oxide semiconductor, or CMOS. And despite being viewed as rivals in the camera industry, each type of image sensor really has its own strengths and weaknesses. So the better sensor depends on the situation it is to be used in.

CCD sensors were developed specifically to be used in cameras and for the purpose of capturing images. CMOS sensors were developed off standard technology already in use, such as memory chips in computers. However, CMOS sensors today are being developed further for the purpose of being in cameras and the image quality it provides is improving.

CCD sensors are still slightly better in light sensitivity and produce cleaner images than CMOS sensors. Because of higher light sensitivity, the CCD produces sharper images in low light conditions than CMOS sensors.

The two downsides to the CCD sensors are really the true advantages to CMOS sensors. The CCDs make the cameras more expensive since they are harder to put into a camera and an equivalent sensor uses almost one hundred times more power than a CMOS sensor.

Recent advancement in technology is quickly making the CMOS sensor a close rival to the CCD sensor in terms of image quality. CMOS based cameras are lower cost because the CMOS sensors make it easier to build the cameras around them.

Relative to the CCDs, CMOS sensors are more flexible to integration possibilities and functions and have a faster readout. They also require less energy and require a smaller system size. Megapixel CMOS sensors are much more common commercially than megapixel CCD sensors and much less expensive.

In megapixel cameras, the sensors contain over one million pixels, hence the name. To reduce the cost, the sensors are around the same size as VGA sensors meaning the size of each pixel is reduced greatly. This smaller size allows the camera to produce high resolution images with more details but also makes the camera less light sensitive. Since each pixel is smaller in size, and the light reflected from the object is spread across more pixels, it requires better lighting conditions to produce an image.

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