There are several filters commonly used in license plate recognition systems:

1. Infrared cut-off filter:

License plate recognition system at night or in low light environment, in order to enhance the recognition accuracy, will use infrared light source to illuminate the license plate. Infrared cut-off filters can prevent unwanted infrared light from entering the camera, thereby improving the contrast and clarity of the image, which helps in the recognition of the license plate.

2. Uv cut-off filter:

The UV cut-off filter can prevent ultraviolet light from entering the camera and avoid the effect of ultraviolet on the camera image.

3. Visible light cut-off filter:

Visible light cut-off filters can prevent certain wavelengths of visible light from entering the camera, helping to eliminate the impact of light conditions on image quality and improve the clarity of the image.

4. Narrow band filter:

Narrow band filters can pass through specific wavelengths of light, thus reducing the impact of stray light on the image. In the license plate recognition system, narrow-band filters are usually used to reduce the interference of background light or reflected light and improve the signal-to-noise ratio of the license plate area.

5. Polarization filter:

The polarizer can reduce the influence of reflected light on license plate recognition and improve the quality of license plate image. In some cases, polarizers are used with infrared cut-off filters to enhance license plate recognition.

In summary, the license plate recognition system will choose the appropriate filter according to the actual application needs to improve the imaging quality and recognition effect. These filters can be used alone or in combination. Different filters can be targeted to solve the imaging problem in different environments, thereby improving the overall performance of the license plate recognition system.