Image sensor is the core component of any camera. Conventional analog cameras adopt interlaced CCD image sensor to capture standard definition images, while recent network cameras utilize progressive scan CMOS image sensor to deliver high definition images. The quality of image sensor determines the camera's imaging capability and performance. In this article, we intend to give you some basic information about image sensor.
Image sensor is the "eye" of your security camera. An image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. An image sensor is typically a charge-coupled device (CCD) or a complementary metal–oxide–semiconductor (CMOS) active-pixel sensor.
CCD and CMOS image sensors are two different technologies for capturing images digitally. Both types of imagers convert light into electric charge and process it into electronic signals.
CCD is the abbreviation of Charge Coupled Device, is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated. To integrate with a sensor, such as a photoelectric device to produce the charge that is being read, thus making the CCD a major technology where the conversion of images into a digital signal is required.
CMOS stands for Complementary Metal-Oxide Semiconductor, also known as active-pixels sensors. CMOS sensor descends from the MOS activepixel image sensor which was invented in the 1960s. Contains integrated circuitry, arrays of pixel sensors.
|Signal out of pixel||Electron packet||Voltage|
|Signal out of chip||Voltage (analog)||Bits (digital)|
|Signal out of camera||Bits (digital)||Bits (digital)|
From above comparison table, we know CCD and CMOS have pros and cons. Based on this, we can choose either CCD or CMOS security cameras for different video surveillance applications.
1. Low light conditions may use CCD camera
Since the CCD sensor has large effective imaging area, under low light conditions, it can receive more light to capture images. That's the reason why CCD image sensor has better low light performance than CMOS image sensor. For low light environments, such as dimly lit parking lot, stairwells, darkroom, user may choose to use CCD cameras.
2. Using CMOS camera in covert environment
The dimension of CMOS image sensor can be very small, therefore the camera can be compact size. However, the CCD camera is limited to its periphery of complex circuits, its dimension cannot be miniature like CMOS. For some places where cameras are vulnerable to vandalism, users may choose to use hidden CMOS camera.
3. CMOS camera for high-speed frame rate
CMOS image sensor can directly convert photoelectric signal to digital signal, processing speed is very fast. This advantage enables CMOS image sensor become very useful for high-speed frame cameras, the ideal speed can reach 400-2000/second. So for the high-frame speed video shooting, use CMOS camera better.
No matter how good CCD is, or how fast development of CMOS technology, CCD imaging technology is still monopolized by Japanese companies (Sony, Panasonic, Sharp etc). For high definition security cameras, American companies control the video processing, video compression and transmission etc technologies. Therefore, first developed high definition network cameras adopts CMOS image sensor + Texas Instrument (TI) solution. Additionally, CMOS sensors are much less expensive to manufacture than CCD sensors. To manufacture CMOS image sensor require a total different manufacturing infrastructure. In the past years, CCD image sensor manufacturers were reluctant to abandon CCD sensors manufacturing. More and more security companies choose to develop network cameras equipped with CMOS image sensors.
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