Fog penetration algorithms known to people during shopping spree can be roughly divided into two categories: one is a non-model image enhancement method, which enhances the contrast of the image and meets the subjective vision requirements to achieve the purpose of clarity; the other One is a model-based image restoration method, which examines the causes of image degradation, models the degradation process, and uses reverse processing to finally solve the problem of image restoration.

The difference between electronic fog penetration and optical fog penetration 1. Electronic fog penetration technology
When the security demand develops from passive detection to active defense, various image processing algorithms that intelligent analysis relies on become important. Among them, fog-through processing integrates a variety of image algorithms, which is a more important type of image processing technology. Currently known fog penetration algorithms can be roughly divided into two categories: one is a non-model image enhancement method, which enhances the contrast of the image to meet the subjective vision requirements to achieve the purpose of sharpening; the other is model-based image The restoration method, which examines the causes of image degradation, models the degradation process, and uses reverse processing to finally solve the problem of image restoration.

In order to get better processing results, camera manufacturers will add a special image processing chip that can automatically detect the density of the image, keep the details of the image signal to the maximum, and achieve color enhancement, contrast enhancement, edge enhancement, contrast enhancement and brightness enhancement , And perform operations such as density segmentation and deblurring, so that the image quality of the camera in different scenes is significantly improved, and the purpose of fog penetration is achieved. According to the manufacturer's capabilities and R&D choices, different chips such as DSP or FPGA will be selected for corresponding processing.

The chip will read the video stream information in real time, and determine whether the fog-through mode needs to be turned on by comparing the parameters, that is, it can automatically detect the fog, and even determine the fog density through the preset mode, and choose to enter the corresponding fog-through mode .

The difference between electronic fog penetration and optical fog penetration 2. Optical fog penetration technology
Natural light is composed of light waves with different wavelengths. The visible range of the human eye is roughly 390nm-780nm. The wavelengths from long to short correspond to seven colors of red, orange, blue, green, green, orange and purple. Among them, the wavelength less than 390nm is called ultraviolet, and the wavelength is greater than 780nm. Is called infrared. Different wavelengths of light have different characteristics due to different wavelengths. Fog and smoke affect visible light imaging. Because infrared has a longer wavelength, it 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 of optical fog penetration.

1、lens
From the principle, it can be known that the focus of optical fog penetration is to intercept and accurately focus light in a specific near-infrared band, and most of this part of the work is done by the lens. It can be said that the quality of the lens determines the effect of optical fog penetration. The difficulty of lens design lies first in the optical design, including the grasp of the optical path and the selection of filters, and secondly, the material selection and process technology also determine the effect of the finished product. The biggest difference between the fog lens is that it can carry the width of the infrared band, that is, the latitude of the focal plane. In principle, the wider the available near-infrared band, the better, but limited by the difficulty of lens optical path design and the sensitivity of CCD, the longest infrared band that can be utilized by the current security industry lenses is known to be 1100nm.

2、filter
Those who know day and night conversion cameras are not unfamiliar with filters. Generally, this type of camera is equipped with two filters, one is responsible for filtering out light waves other than visible light during the day, so that the image is clearer and brighter; the other is used at night and is responsible Release the infrared band that the CCD can carry to realize infrared monitoring at night.

The professional fog-through lens has a built-in highly targeted filter, which is used to accurately intercept the light of the required band. In order to adapt to specific environmental conditions, multiple filters for different bands are often loaded and linked to the camera through the 485 interface , Realize switching.

The difference between electronic fog penetration and optical fog penetration 3. Development analysis of the two technologies

(1) The bottleneck and development of optical fog penetration technology
Because the near-infrared light that can penetrate the haze is directly used for imaging, although the optical fog can only obtain black and white monitoring images, its imaging effect is outstanding, and it has also been used in maritime and ocean. Due to high cost constraints, although large-scale projects such as Safe City and even the civilian market have seen a certain amount of fog penetration in recent years, the actual number is still limited.

At the same time, because the technology is more mature, it needs to find another way to achieve better fog penetration by relying on the lens or optics. In the short term, it is difficult to extend the wavelength tolerance of the lens beyond 1100nm, but if visible light is not taken into account, it can be extended in the near-infrared band; therefore, you can consider loading two sets of lenses in one set of equipment, and use them under normal conditions. For visible light lenses, special fog-through lenses are used in foggy days, which not only preserves the color images of visible light, but also improves the latitude of fog-through lenses and realizes multi-screen contrast monitoring.

(2) The emergence of an all-in-one movement helps electronic fog penetration
With the diversification of products and the continuous maturity of the market, the emergence of integrated mist-permeable movement can be said to be of great significance to the popularization of mist-permeable products. Most of the all-in-one movements released in recent years use pure electronic fogging, and carry out arithmetic processing through the embedded FPGA chip. It can output color images. This algorithm can distinguish factors such as the fog density in the distant and near fields, and improve each pixel to achieve the best regional effect. It is different from the overall improvement of the picture contrast in the past, and there is no delay. Moreover, the high-speed operation of the chip will inevitably produce noise points, and the impact will be more prominent when the night light is insufficient. The integrated fog-through movement generally uses CCD sensors and large aperture lenses to achieve good low-light effects. On the other hand, it is easier to achieve high-definition fog-through.

In the past, the demand for fog penetration was basically in the camera, but the monitoring distance of the camera is generally short, and if it is not thick fog in a short distance, the picture will not have much impact. And the monitoring range of the integrated machine is larger, and the zoom is optional, so the haze has a greater impact on it. The emergence of the integrated mist-permeable movement is to achieve mist penetration in a larger monitoring distance, and with the finished product, the integrated mist-permeable movement will reduce the investment of mist-permeable equipment and achieve greater applications.