13 Low-Light Video Surveillance Tips to Enlighten Your Solutions
Distinguish Among Types of Technologies
Even though low-light cameras have varying labels, they contain the same fundamental components: a lens and sensor along with some level of image processing. These are not be confused with thermal cameras or cameras with IR illuminators, which are quite different.
The most common low-light cameras use an IR cut filter, which accounts for 90% of the market, according to White. An IR cut filter is a mechanical filter that sits between the lens and the sensor (CMOS chip) and cuts out IR illumination during the day to improve color quality.
It is called a cut filter because it filters out, or “cuts out” IR during the day. At night it slides out of the way to allow more light to get to the sensor, which improves low-light video quality.
When the IR cut filter is out of the imaging path, the image is monochrome without color. In most cases, the filter is mechanically driven by algorithm, but in some cameras, it can be manually controlled.
But if almost all cameras on the market contain IR cut filters, what distinguishes one from the next? The lens and the processing.
The lens transmits light to the sensor, and the data on the sensor is encoded and processed by a processor. The variance among cameras is often in the optics (lens).
According to Ryan Zatolokin, senior technologist at Axis Communications, it is important to use an IR-corrected lens, which costs more.
“If you do not use an IR-correct lens, then the flow of the light comes in a slightly different angle, which causes the image to look blurry even in a static image because the IR light is hitting the image sensor differently than the visible light,” he notes.
Says White, “If you have cheesy optics in front of the IR filter, you are not going to get much quality out of that camera and will have wasted the money on the sensor.”
There is a wide variety of sensor capabilities. Most premium-branded manufacturers of low-light products use the highest quality sensor they can. Many imaging sensors are supplied by the same manufacturers, including Sony, Panasonic and Aptina (now ON Semiconductor), and bought by various camera manufacturers, in some cases to address certain applications.
According to Robert Mitchell, director government practice and law enforcement for IC Realtime, Sony’s new Starvis sensor technology, for example, is designed for industrial applications.
Other improvements in technology have been occurring. Cameras are manipulating the light by doing things like increasing the time at which the lens is open so it can absorb more light.
This can even be done to the point of allowing the camera to retain even a color image at night.
“But while that allowed you to have a color image at night, it had some negative things associated with doing that,” says Alex Petrao, director of products for surveillance at SnapAV. “When you have the aperture open longer, you get this time-lapse effect where any movement would be blurred, and you see a trailing image. Now, you’re starting to see some significant improvements in the sensors being used, so that they’re able to just pick up very low amounts of light and still be able to retain a color image.”
None of this should be confused with thermal cameras, which are another type. Market leaders like FLIR offer thermal cameras, which are devoid of color and can be used to detect people from a long distance, even up to 1 kilometer away.