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  1. CCTV SYSTEMS • CCD VERSUS CMOS COMPARISON • CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors are two different technologies for capturing images digitally. • Each has unique strengths and weaknesses giving advantages in different applications. • Neither is categorically superior to the other, although vendors selling only one technology have usually claimed otherwise.

  2. CCTV SYSTEMS • In the last five years much has changed with both technologies, and many projections regarding the demise of either have been proved false. • The current situation and outlook for both technologies is vibrant. • Both types of imagers convert light into electric charge and process it into electronic signals.

  3. CCTV SYSTEMS • In a CCD sensor, every pixel's charge is transferred through a very limited number of output nodes (often just one) to be converted to voltage, buffered, and sent off-chip as an analog signal. • All of the pixel can be devoted to light capture, and the output's uniformity (a key factor in image quality) is high.

  4. CCTV SYSTEMS • In a CMOS sensor, each pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise-correction, and digitization circuits, so that the chip outputs digital bits. • These other functions increase the design complexity and reduce the area available for light capture.

  5. CCTV SYSTEMS • With each pixel doing its own conversion, uniformity is lower. • But the chip can be built to require less off-chip circuitry for basic operation. • CCD sensors, as mentioned above, create high-quality, low-noise images. • CMOS sensors, traditionally, are more susceptible to noise.

  6. CCTV SYSTEMS • CCDs use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor. • CCD sensors have been mass produced for a longer period of time, so they are more mature. • They tend to have higher quality and more pixels.

  7. CCTV SYSTEMS • Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. • Many of the photons hitting the chip hit the transistors instead of the photodiode. • CMOS traditionally consumes little power. Implementing a sensor in CMOS yields a low-power sensor.

  8. CCTV SYSTEMS • CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors. • Based on these differences, you can see that CCDs tend to be used in cameras that focus on high-quality images with lots of pixels and excellent light sensitivity.

  9. CCTV SYSTEMS • CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. • CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. • CMOS cameras are usually less expensive and have great battery life.

  10. CCTV SYSTEMS • CCD technology: • The light gathering area of a typical CCD is only a few millimeters on each side, but contains 400,000 or more light sensitive photo-sites.

  11. CCTV SYSTEMS • To process and redistribute color information, the CCD in your camera has to measure light at three separate wavelengths of red, green, and blue. • In other words, it has to be able to recognize color. It does so through use of a CCD Array, which is a device that mounts charge-coupled devices together to capture more pixel information.

  12. CCTV SYSTEMS • Single CCD array technology uses exactly what the name implies, just one CCD array to process all color information. • This low-cost technology employs use of a grid of color filters on the face of the array so that only red, green, or blue light ever reaches any given pixel.

  13. CCTV SYSTEMS • As the need for high-quality video imaging grew, three chip color cameras made their way into the market. • For this technology to work, a complex optical prism assembly is used to separate the image being captured into three components: red, green, and blue. • Because of the prism assembly, each of the three colors gets its own charge-coupled device.

  14. CCTV SYSTEMS • This means almost all of the light information associated with a particular color channel is captured by its own array and the individual CCD is able to devote all of its pixels to that particular color channel, unlike single CCD technology where just one array has to process and split all of the color information.