Ahmed Shakib - Technician – 2M CCTV
Cameras these days range from security surveillance to your average point and shoot cameras. If you strip the hardware that makes up the camera and the lens that lets you see the world, you will notice little reflective photodiodes which make up a device called an image sensor. Depending on the specs of your security camera, you will notice that it has one of the following two image sensors inside: CCD (charged-coupled device), or CMOS, (complimentary metal-oxide semiconductor). CCD and CMOS are types of photodiodes that are integrated into solar panels and, essentially, they perform very similar tasks to one another. They convert light to electrons, and transform it into an image, where it can be read or displayed.
Note that both CCD and CMOS use the typical dimension to measure the size of their image sensor: 1/3″, 1/4″, and etc.
Since CCD moves its charged cells across the chip, it is less prone to distortion, but consumes more power. This leads CCD image sensors to produce higher quality images, have higher sensitivity to light, and produce far less noise than CMOS devices. The main reason CMOS devices have lower video quality and higher image noise is due to the fact that each pixel has dedicated transistors which sit very close to the CMOS sensor. Light that is captured by the photodiodes are also touching the transistors, which in turn make it lose its image quality.
CCD works differently letting its charged cells across the array, and makes use of external devices to process its signal. This external device could be a digital converter like a DVR, or a building signal processor. This external device allows the charged cells to be converted from analog to digital signal by matching each pixel value to a digital value. Because it yields higher quality images and much lower noise within the image, the CCD image sensor is very popular within the CCTV & surveillance industry.
The technologies behind CMOS have gone through extensive improvements, which have lowered the prices for the average cameras drastically. The few “cons” I have mentioned have also improved along the way. The quality of images taken with the CMOS sensor (after recent technological advancements) cannot be distinguished from those taken with a CCD device with our naked eye. Nevertheless, the advantages of having a CMOS device outweigh the benefits of the CCD device.
Unlike CCD, the CMOS image sensor has transistors at each pixel that amplify the charged electrons across the X-Y wires, making it consume less power than CCD devices (about 100 times less power). In addition, the CMOS image sensor is more flexible than CCD, because each pixel is read individually.
The production of CMOS is very cost effective. CMOS image sensors can be produced and shipped in less time than CCD image sensors. You could manufacture a CMOS chip, as its semiconductor, with 90% of the manufacturers that produce computer chips or other semiconductor chips. CCD sensors rely on special machines to manufacturer the sensor chip and at times require many different facilities to complete one production, making it more costly to produce.
Image Scanning Technologies (Progressive and Interlaced)
CCD and CMOS sensors found inside security cameras come with advanced built-in technologies that enhance their basic functionalities. Interlaced and progressive scans are few of these technologies. They process the images within the frames, in order to hide flaws that would have been noticeable otherwise.
Interlaced scanning is exclusive to CCD devices. When interlaced images are captured, odd and even lines are created, which are then alternated 25 (PAL) or 30 (NTSC) frames per second. The switching between odd and even lines is done so fast, that it can not be detected by the naked eye.
Progressive scanning is common to CCD and CMOS, but is mainly used by CMOS security cameras. Progressive scanning allows the camera to obtain values from each pixel in the sensor and scans them consequently, in order to produce a complete picture. This is very important in a security camera, because interlaced and progressive scanning allow the DVR to record more fluid footage, and avoid the distortion created by a moving car or the leaves of a tree.
Since their induction in the 1900s, CMOS devices have come a long way and became a driving force for the overall camera industry. CCD devices will still be used with the next generation of analog security cameras, because of their ability to achieve higher resolutions. CMOS devices are capable of processing higher quality images and are used primarily on megapixel cameras, because of their higher shutter speed and lower power usage. Whether you buy a camera that has a CCD image sensor or CMOS image sensor, please note that looking at the live video on the security monitor will not allow you to distinguish between the two.