Image Sensors for Security Cameras - CMOS vs CCD

24/09/2015 0 Comment(s) Surveillance Equipment,

Security cameras are equipped with either a CMOS or a CCD sensor. There are distinct differences as well as advantages in using either of these camera-imaging options, and end users of security products should take note of these differences when choosing the units to deploy in their security systems.

How a CMOS sensor works

Complementary metal oxide semiconductor (CMOS) is an image sensor for digital security cameras that employs digital signal. IP surveillance cameras use CMOS image sensors to transmit signals through a local area network (LAN), which the network video recorder (NVR) processes and then stores.

The CMOS sensor incorporates other circuits on the same chip, allowing additional on-chip features at minimal extra cost and uses pixel level circuitry. CMOS-based cameras have rolling shutters, which means that instead of image frames being exposed all at once, exposure is from one side to the other. The exposure process results to some distortion of the digital imagery or sensor artifacts. Users of security cameras with CMOS sensor can easily spot these artifacts in the video footages from their security system.

  • The skew from the rolling shutter is observed when the subject (or camera) is moving during exposure. The side-to-side shutter recording can make an object appear several times in the image, or will result to some distortion. For example, if the recording is from top to bottom and the subject moves across the frame, you will observe that the lower body stretches out in front of the head and torso.
  • The wobble, also called the Jello effect, make images appear to be stretched or duplicated.
  • Partial exposure happens when the camera flash or any flash of light is caught in the shot. Images may appear divided by a sharp line, with one side clearly lit by the flash.


Brief comparison of CMOS and CCD

The performance of the CMOS image sensor is sometimes compared to that of the Charge-Coupled Device (CCD) image sensor that adopt analog signals, which is found in the traditional security cameras. Image detection for CMOS and CCD starts with the conversion of light into electrons through technologies that vary for each manufacturer of security cameras. In CCD imaging, an analog-to-digital converter converts each pixel into a digital value. In a CMOS-based camera, transistors that are present at each pixel perform the task of amplifying and moving electrons through the wires, making the process more flexible since every pixel is read individually.

There are pros and cons that make some security experts prefer one type of sensor to the other, but most agree that the CMOS sensor has the advantage of a simpler structure, lower cost, and lower power consumption. Electronic data for CMOS sensors is contained in a single chip that utilizes minimal space and operates with less power, which is one reason why most cell phones are equipped with CMOS cameras. However, CCD sensors produce better image quality, though technology advances for CMOS have considerably narrowed down the quality differences. 


Advantages of using CMOS sensors

Manufacturers of surveillance cameras are looking into other factors that impact on image quality other than the sensor employed. The image processor and the processing technology contribute as much in producing high quality images, and can make up for any shortfall that may be observed when using a CMOS camera, which are more cost effective than the traditional CCD cameras.

  • The advantages of using CMOS sensors lie in cheaper manufacturing costs and low energy consumption that translate to lower prices for security cameras and lower cost of security operation.
  •  CMOS cameras have the advantage of speed, which is an important feature for video surveillance cameras. The continuing efforts of camera manufacturers to develop and integrate high-speed video capture mode in CMOS-based security cameras will highly affect the quality of security footages for end users.
  • CMOS-based cameras have autofocus and video capture capabilities that can be harnessed to improve security systems. Some features that can be built into the CMOS-based camera include high speed video capture of up to 60 frames per second at 1080p, and motion-controlled panorama modes.
  • CMOS-based cameras perform well in low-light shooting. The backside-illuminated CMOS sensor is finding its way into security cameras due to improved low-light performance. Also called backside illumination (BSI) of back-illuminated sensor (BI), the technology increases the amount of light capture through an innovative arrangement of the imaging elements.


A comparison of CCD-based and CMOS-based cameras will give users a clearer picture of the major pros and cons in using each image sensor.

  • CCD sensors consume as much as 100 times more power compared to an equivalent CMOS-based camera that employs a low-power sensor.
  • CMOS cameras are susceptible to noise, whereas CCD cameras process low noise, high quality images.
  • The CMOS chip has a lower light sensitivity compared with CCD sensors because the electrons entering the sensor hit the transistors rather than the photodiode. The CCD sensor sees images under 0.1 to 3 Lux light conditions, while the CMOS sensor requires 6 to 15 Lux, with up to 10 times higher noise ratio. Thus, CCDs are the preferred sensors for video surveillance cameras.  This factor has been partly addressed by the novel re-arranging of the imaging elements for the BSI sensor that resulted to an improved performance in low-light shooting.
  • The CCD technology is more mature and has been mass-produced for a longer time, resulting to more pixels that translate to higher quality of images.
  • CMOS chips are easy to manufacture in any electronic assembly line, and are therefore much cheaper than CCDs.

Briefly, the CMOS sensor has the advantage of cost, while the CCD sensor has quality on its side. However, with technology advances, the CMOS can catch up and even out or come closer to the quality of imaging associated with CCDs.



The CMOS and CCD image sensors have inherent differences in technology and performance but advances in each technology are narrowing the difference gap. Users of security cameras will perceive the differences according to how these impacts on their security systems, in terms of cost and image quality.


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