Brief analysis on the relevant principles of infrared camera night application

Before talking about infrared cameras, let's talk about some basic knowledge. The wavelength of visible light is generally 0.4 to 0.7 microns, which is the light that the eyes can see. The section from 0.7 to 400 microns is infrared light, which is invisible light and beyond the range that the human eye can see. In addition, any object above absolute zero will emit thermal radiation infrared light, and heat-generating objects such as the human body will emit more infrared light than houses, trees, stones and other objects.

The camera sensor CCD or CMOS, also known as "Sensor", is a semiconductor device that converts optical images into digital signals. But what is more powerful than the eyes is that it can sense some invisible light, such as infrared light. The sensor has an indicator sensitivity, also called the minimum illumination value, which is the ability to respond to weak light. The higher the sensitivity, the stronger the ability to sense light and the stronger the ability to sense infrared.

Since the sensor can sense infrared rays, during the day, infrared rays in the light also enter the sensor, causing the overall image to be reddish. Therefore, ordinary cameras have filters on the surface of the sensor to filter out infrared rays in the light. If the infrared camera is also attached with such a filter, the infrared rays actively emitted by the infrared lamp of the camera at night will also be filtered out, causing the infrared lamp to fail. To avoid this situation, high-end infrared cameras are generally equipped with dual filters, that is, the infrared filter is turned on during the day to filter out infrared rays in the light, and the infrared filter is turned off at night to allow the infrared rays of the fill light to enter the image through the lens .

The above is why infrared cameras can produce clear images at night when human eyes cannot see clearly. Relying on the characteristic of infrared camera sensors that can sense infrared rays, in the environment with poor light at night , infrared fill light or infrared thermal radiation of the object itself is used to achieve night vision, and dual filters are used to ensure that the image during the day is not color-biased.