The size of the infrared image signal depends on the temperature difference between the external scenes, and its radiance distribution is mainly determined by the temperature and emissivity of the observed scene, that is, the infrared image approximately reflects the temperature difference or radiation difference of the scene, so it has the following advantages:

1) It is more suitable for observing low-visibility targets with large thermal contrast with the background.

2) "all-weather" and "all-passive" observation can be achieved, and objects can emit radiation even in complete darkness and fog to form infrared images.

3) The observation distance is long.

For natural scenes, in a local range, due to the tendency of thermal equilibrium, this temperature difference cannot be very large. At the same time, because the infrared radiation of the target and the background needs to pass through atmospheric transmission, optical system, photoelectric conversion and electronic processing, etc. It is converted into an infrared image, which determines the poor ability of the infrared sensor image detail, as shown in the figure below.

Ideally, when the infrared detector is exposed to uniform infrared radiation, the output signal amplitude of each pixel should be exactly the same.

Infrared imaging systems are sensitive to thermally radiating objects, with low thermal detail contrast and high dynamic range.

are often limited and lose their natural appearance at different target background temperatures. In addition, the non-uniformity of the thermal imaging system is also a large interference factor.

In fact, due to the non-uniformity, mask error, defect, process and other factors of the semiconductor material used to make the infrared detector device, the output amplitude will appear non-uniform, making the acquired image signal blurry and distorted. Even make the sensor lose the ability to detect.

In summary, infrared images have the following disadvantages:

1) Infrared thermal images represent the temperature distribution of the scene, are grayscale images, have no stereoscopic effect, and have low resolution to the human eye.

2) Influenced by the thermal balance of the scene, wavelength, long transmission distance, atmospheric attenuation and other factors, the infrared image has strong spatial correlation, low contrast, and blurred visual effect.

3) The detection capability and spatial resolution of the thermal imaging system are lower than those of the visible light CCD array, so that the clarity of the infrared image is lower than that of the visible light image.

4) The random interference of the external environment and the imperfection of the thermal imaging system bring a variety of noises to the infrared image, such as thermal noise, shot noise, 1/f noise, and photon electron fluctuation noise.