Selecting the right camera for security applications is far more complicated than what one would think. It is not just selecting the right camera; lens technology and image processing technology are also factors to be considered, as well as whether quality pictures are possible in low light conditions; or whether the image processing technology can handle an image with both bright sunlight and heavy shadows.
The belief that just any IP camera, like the one on a PC or built into the laptop for a Skype video call, will do as a security camera is a misconception.
The performance of a digital camera is largely determined by three key components: the lens, the image sensor (CMOS or CCD), and the image processor.
The image sensor, which takes the light entering the camera through the lens and converts it into electrical signals, can be compared to the film used in a traditional film camera, while the image processor “develops” the image. If any one of these three components is of substandard quality, it will negatively affect the images that the camera produces.
“The main difference between various cameras used in security applications boils down to how the lens is made and the sophistication of the image processor,” says Braam Steyn of Canon South Africa.
“The best lens option is a lens that includes aspherical elements to give best imaging across the whole zoom range. The technology allows the lens to be made more compact, but also has several design advantages.”
An aspherical lens has a more complex surface profile that can reduce or eliminate spherical aberration. This is an optical effect that occurs due to the increased refraction of light rays when they strike a lens or a reflection of light rays when they strike a mirror near its edge, in comparison with those that strike nearer the centre. It also reduces other optical aberrations compared to a simple lens. Lens coatings also play an important part in ensuring minimum unwanted reflections.
“We use two image processors in our security cameras,” said Steyn. “The one to process the image and the second one to turn the images into the IP format for streaming on the network.”
The evolution of the DIGIC image processor has been the result of an ongoing search for better levels of image quality and faster speeds. Today’s DIGIC image processor does more than mere image processing: It controls a wide range of functions and circuits, including automatic exposure control, exposure mode control, image file compression/playback control, LCD display control, and more. All of these functions are contained in a single-chip system large-scale integrated circuit (LSI).
In security applications the ability to capture images in a variety of light conditions is an important consideration. The ideal camera must be able to capture images in very low light conditions but also where an area to be monitored is illuminated by full sunlight. The third challenge is to view images in area that is contrasted with bright sunlight and shadows.
Can a person walking along a wall in a dark shaded area still be observed when he steps out of the shade into full sunlight? The same applies at night, when in many instance some areas are floodlit but there are also spots in deep shadow. “It is all a function of the lens and the image processor,” says Steyn. “It is therefore important to discuss which camera is best suited for which application with a professional security consultant.”
Another important aspect when selecting a camera is the angle it will cover. If a camera is mounted in the corner of a room, will it cover the whole room and will the entire image be in full focus? There are cameras today that can do that.
Steyn also pointed out an important feature: the remote positioning of the camera. Some of the less expensive cameras have to be set up by a technician and cannot be remotely positioned, angled or focused.
These cameras require someone on top of the ladder to keep adjusting the camera with someone looking at the screen and giving instructions. A remote positioning and focus control facility is almost indispensable, enabling one person to position the camera and adjust the focus from a PC, integrated into a security system or remotely from a tablet or smartphone.
In some applications is it may necessary to be able to read number plates. A prerequisite is a good camera with ample telephoto or zoom abilities and the right software for the purpose.
There are as many different cameras on the market as applications. As Steyn said, “Consult an expert before purchasing a camera-based security system.”