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 Day Night functionality

Day & Night functionality

Role of an infrared-cut filter in a camera

Certain environments or situations restrict the use of artificial light, making infrared (IR) cameras particularly useful. These include low-light surveillance applications, where light conditions are less than optimal, as well as discreet and covert surveillance situations. Infrared-sensitive cameras, which can make use of invisible infrared light, can be applied, for instance, in a residential area late at night without disturbing residents. They are also useful when the surveillance cameras should not be evident.

Light perception

Light is a form of radiation wave energy that exists in a spectrum. The human eye can see, however, only a portion (between wavelengths of ~400 – 700 nanometers or nm). Below blue, just outside the range humans can see, is ultraviolet light, and above red is infrared light.

     

Infrared energy (light) is emitted by all objects: humans, animals and grass, for instance. Warmer objects such as people and animals stand out from typically cooler backgrounds. In low light conditions, for example at night, the human eye cannot perceive color and hue -- only black, white and shades of gray.

How does the day and night functionality or IR-cut filter work?

While the human eye can only register light between the blue and red spectrum, a color camera's image sensor can detect more. The image sensor can sense long-wave infrared radiation and thus "see" infrared light. Allowing infrared to hit the image sensor during daylight, however, will distort colors as humans see them. This is why all color cameras are equipped with an IR-cut filter -- an optical piece of glass that is placed between the lens and the image sensor -- to remove IR light and to render color images that humans are used to.

As illumination is reduced and the image darkens, the IR-cut filter in a day & night camera can be removed automatically* to enable the camera to make use of IR light so that it can "see" even in a very dark environment. To avoid color distortions, the camera often switches to black and white mode, and is thus able to generate high quality black and white images. The IR-cut filter in Axis' day & night cameras can also be removed manually via the cameras' Web interface.


IR-cut filter in place

IR-cut filter removed
 
IR light is filtered away in the camera by an IR-cut filter in order to render color images that humans are used to. When light conditions are too dark to render color images, a day & night camera's IR-cut filter can be removed to enable the camera to make use of IR light to produce high quality black & white video. 

 
For more information, see also:


* The ability to automatically place or remove the IR-cut filter in front of a camera's image sensor depends on the make of the camera.

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