Every CCTV camera has an image sensor. This sensor is made up of many photosites and each of these photosites corresponds to a pixel. Each pixel measures the amount of light it is exposed to and converts it into a number of electrons. The brighter the light, the more electrons that are generated.
There are two main technologies used in a cameras sensor.
CCD stands for charged-coupled device. CMOS stands for complementary metal-oxide semiconductor. Each type of image sensor has its strengths and weaknesses depending on the type of application they are used in. CCD sensors are produced using technology specifically developed for the camera industry. CMOS sensors are based on technology used in memory chips in computers. Which one is best? This proves an elusive answer as markets and technologies evolve constantly. Some applications are best served by CMOS sensors while others are better served by CCD sensors. This is why we explain all the differences so you can best decide which is the right one for the right situation.
CCD image sensors have been used in cameras for over 30 years. They offer slightly better sensitivity while producing less noise than CMOS sensors. Higher light sensitivity translates into better images in low light conditions, however the trade offs are that they are more expensive and consume far more power, up to 100 times the equivalent CMOS sensor.
CMOS images sensors lowers the total cost for cameras and more recent advances mean that the image quality is almost as good as the CCD equivalent. They have a faster readout, lower power dissipation and smaller system size.
Image sensors by definition convert electrons into voltage. However, there are different ways to get from point A to point B. A CMOS sensor has circuitry at every photo sensor. So each pixel is read simultaneously and then transmitted as digital information at once. This set up leaves the chip relatively crowded with circuitry but is extremely efficient. In a CCD imager, the pixels are recorded on the chip and then one by one sent through the analog to digital converter to build the data. This takes more energy than the CMOS process, but delivers much cleaner images.
Because CMOS sensors convert visual information to digital information so efficiently, the power required to operate these devices is relatively low. In a CCD camera, the amount of work required to convert all the pixels to data sucks lots of battery power. Though this may seem trivial to most photographers, the world has many uses for low energy photography. Security cameras, cell phone cameras and most computer electronics would suffer a disadvantage if battery life were a consistent problem for the consumer. These devices are also not necessarily required to deliver pristine images, so they are designed with the cheaper option, CMOS.
CMOS sensors generally record less resolution than CCD cameras because they cannot physically sustain as many pixels on the plane of the chip. Each CMOS pixel is packaged with the circuitry to convert it to a digital signal, thus each sensor takes up more space. Even though a CCD sensor has to spend more time and energy converting each pixel, it can hold more across its surface. So the noise level on a CCD sensor is inherently less than that on a CMOS sensor of the same size. This difference in layout also leads to more dynamic range in CCD sensors. The colors tend to be more saturated and vibrant in contrast to those that are captured through a CMOS sensor.
CCD sensors tend to respond better to low light conditions than CMOS sensors. The clutter on CMOS sensors reduces the light sensitivity of the chip. It takes more light to penetrate the thick layers, so dim light will not make it through. However, the advantage is that CMOS sensors facilitate adding gain to an image. Because circuitry is so close to each pixel, the camera can boost the exposure as it is recorded. On a CCD camera, the image will need to be enhanced through the same energy consuming process as it is recorded. This in turn makes it more difficult for CCD cameras to run efficiently.