An IR filter, or IR cut filter, is a color filter blocking the infrared light. In order to avoid unwanted side-effects caused by infrared light (as part of the natural ambient light) during image capturing in daylight mode, an IR Cut Filter is installed in front of the sensor. The filter is meant to prevent the incidence of infrared light onto the image sensor. When ICR is on, the camera is able to increase its light sensitivity in monochrome mode.
In situations with little or no lighting, a security camera can use infrared light to illuminate the area and the ICR has an important role in that. In this article, you will learn what the infrared cut filter is and what is the meaning of the day/night feature available in professional security cameras.
What is ICR (Infrared Cut Removal)?
Infrared light is a component of daylight. Unlike the eye, CCTV cameras have sensitivities extending into the infrared. During camera operation in the daylight a filter is required to eliminate the infrared wavelengths. With a sufficient amount of natural or artificial light the image recorded by the camera is clear and the colours are rendered correctly. A complete range of visible and infrared wavelengths reaching the camera will affect the colour rendering and overall image quality. Thus, the infrared wavelengths should be limited from reaching the image sensor by a mechanical infrared cut-off filter.
If the illumination is insufficient, the IR illuminator will automatically activate and synchronise the operation of the ICR filter. The IR illuminators arranged around the camera lens emit infrared radiation and illuminate the surrounding monitored by the camera. With the filter open, the camera is sensitive to the IR radiation illuminating the object. As a result, the camera can operate in complete darkness. The camera switches to monochrome mode providing a clear and sharp image.
Depending on the camera model, the filter mechanism operates in different modes. However, the function remains the same. The animation shows the operation of the mechanical infrared cut-off filter in APTI cameras. A click can be heard when the camera switches between the day mode and the night mode.
Almost all new Day/Night cameras for 24h monitoring with CMOS image sensor recording high resolution images include an ICR filter. The interference due to infrared wavelengths should be eliminated to the greatest extent possible. The cameras without a mechanical infrared cut-off filter has this component built-in. A spectral-response characteristic of the camera is practically constant and switching between colour and monochrome images is carried out by an electronic module which also processes the images from the image sensor. Those are mostly analogue cameras with CCD image sensors with an adequate efficiency of image recording at night.
The difference between true and electronic Day/Night
True Day Night security cameras are cameras that contain an IR cut filter (IRC), the CCD sensors on these cameras are sensitive to both IR light radiation and physical light. During the day when you have plenty of physical light, the IR cut filter slides in front of the sensor, blocking the IR light radiation, allowing only visible light to pass thru the lens.
True Day/Night means that the security camera can produce clear video for both light and dark situations. Cameras that do not have this physical filter do the correction of light using an electronic process and therefore are considered cameras with electronic Day/Night (they do not have the IR Cut Filter).
Which Day/Night is the best?
Obviously the “True Day/Night” is the best because there is a physical filter that is used during the day time and automatically removed at night. There’s a mechanical piece there and not just some software algorithm. Cameras that have ICR work much better at night when infrared illumination is used. Our recommendation is to prioritize this feature when purchasing new CCTV security cameras.
The optimum solution is to use a switchable infrared-cut filter. In daylight, the filter covers the sensor to provide colour footage, while at night the filter opens for a brighter image. In industry terms, these cameras are known as day/night or true day/night cameras. So look for this feature on the spec list when researching for CCTV cameras.
