The difference between electronic fog transmission and optical fog transmission

1、 Electronic fog technology

As security needs evolve from passive detection to active defense, various image processing algorithms that intelligent analysis relies on become crucial. Among them, fog processing combines multiple image algorithms and is a relatively important type of image processing technology. At present, the known dehazing algorithms can be roughly divided into two categories: one is the image enhancement method based on the model, which enhances the contrast of the image and meets the subjective visual requirements to achieve clarity; Another method is model-based image restoration, which examines the causes of image degradation, models the degradation process, and uses reverse processing to ultimately solve the problem of image restoration.

In order to achieve better processing results, camera manufacturers will add specialized image processing chips that can automatically detect the density of the image, maintain the details of the image signal to the maximum extent, achieve color enhancement, contrast enhancement, edge enhancement, contrast enhancement, and brightness enhancement, and perform density segmentation, deblurring, and other operations to significantly improve the camera image quality in different scenes, achieving the goal of transparency. According to the manufacturer's capabilities and research and development choices, corresponding processing will be carried out on different chips such as DSP or FPGA.

The chip will read real-time video stream information and determine whether to enable fog mode by comparing parameters, which can achieve automatic detection of fog. It can even determine the thickness of fog through the preset mode and select the corresponding fog mode.

Difference 2: Optical fog transmission technology

Natural light is composed of light waves with different wavelengths, with a visible range of approximately 390nm-780nm for the human eye. The wavelengths correspond to seven colors from long to short: red, orange, blue, green, orange, and purple. Wavelength less than 390nm is called ultraviolet, while wavelength greater than 780nm is called infrared. Different wavelengths of light have different characteristics due to their different wavelengths. Mist and smoke affect visible light imaging, while infrared, due to its longer wavelength, is less affected by aerosols during propagation and can penetrate a certain concentration of mist and smoke to achieve accurate focusing. This is the basis for optical fog transmission.

（1） Lens

From the principle, it can be seen that the focus of optical fog transmission is on capturing and accurately focusing specific near-infrared light, and this part of the work is mostly completed by the lens. It can be said that the quality of the lens determines the effect of optical fog transmission. The difficulty of lens design first lies in optical design, including the grasp of the optical path and the selection of filters. Secondly, material selection and process technology also determine the effect of the finished product. The biggest difference of fog through lenses lies in their ability to carry the width of the infrared band, which is the tolerance of the focal plane. In principle, the wider the available near-infrared band, the better. However, due to the difficulty of lens optical path design and the photosensitive ability of CCD, the longest known infrared band that can be utilized by lenses in the security industry is 1100nm.

（2） Filter

Those who are familiar with day night conversion cameras are familiar with filters. Generally, this type of camera is equipped with two filters, one of which is responsible for filtering out light waves outside of visible light during the day, making the imaging clearer and brighter; An application at night, responsible for releasing infrared bands that CCD can carry.