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Friday, June 12, 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.

The CCD, or charge-coupled device, and the CMOS, or complementary metal-oxide semiconductor are often viewed as rival technologies. However, each actually has its own strengths and weaknesses so that one is more appropriate than the other depending on the application.

CCD sensors were developed specifically for the camera industry while CMOS traces it's beginnings to standard technology already in use in areas such as memory chips inside PCs. Today, modern CMOS sensors are advancing in technology and the quality is improving immensely.

The main benefit of a CCD sensor over a CMOS sensor is the higher light sensitivity. Being more sensitive to light means it can produce a better image in conditions where lighting is low.

The problem with the CCD sensor is that it makes the overall cost of a camera more expensive because it is harder to put it inside a camera. The CCD sensor also uses about 100 times more power than a CMOS sensor of equal capacity.

In contrast, the CMOS sensors are quickly over taking the areas that CCD sensors once ruled in terms of image quality. CMOS based cameras always had the edge when it came to cost. It is much easier to build a camera around a CMOS sensor.

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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