At present, in China's large-scale surveillance camera project areas, natural conditions such as rain, steam, haze and other natural conditions easily lead to ambiguity in monitoring, and even in severe cases, there is only a white mist. The fog problem has become a weakness of monitoring equipment. However, in the special monitoring projects, it is very necessary to solve the fog problem, so the current monitoring project puts forward new requirements for the fogging technology. At present, the way in which monitoring equipment realizes fogging can be roughly divided into two types: electronic fogging and optical fogging.
First, the electronically fogging technology intelligent analysis image processing algorithm has become a common application in the camera chip, which through the fog treatment is a collection of a variety of image algorithms, is an important class of image processing technology. One is a non-model image enhancement method that achieves the purpose of clearness by enhancing the contrast of the image to satisfy the requirements of subjective vision; the other is a model-based image restoration method that uses reverse processing to solve the image restoration problem. The chip will read the video stream information in real time to detect the fog, and determine whether the fog-through mode needs to be turned on by comparing the parameters to achieve automatic opening.
Second, the optical fog technology natural light from the combination of different wavelengths of light waves, visible range of the human eye is roughly 390nm-780nm, wavelength greater than 780nm called infrared. Different wavelengths of light have different characteristics because of different wavelengths, and fog and dust may affect the visible light imaging. Infrared rays, because they have longer wavelengths, are less affected by aerosols during propagation, and can penetrate certain concentrations of haze and smoke. , To achieve accurate focus, this is the basis of optical fog.
(I) The principle of the lens is that the focus of optical fogging is the interception and accurate focusing of light in a specific near-infrared band, and most of this work is done by the lens. It can be said that the quality of the lens determines the effect of optical fogging. The difficulty of the lens design lies in the optical design, including the grasp of the optical path and the selection of the filter. Secondly, the selection of materials and technology also determine the effect of the finished product. The biggest difference of the fog lens is that it can bear 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. At present, the longest infrared band available for use in lenses in the security industry is 1100 nm.
(B) filter day and night conversion camera is generally equipped with two filters, one responsible for filtering out the visible light in the daytime outside the light wave, so that the image is more clear and bright; one application at night, is responsible for the release of the CCD can carry the infrared band, to achieve Night infrared surveillance. The professional fog lens incorporates highly targeted filters. The function is to precisely intercept the light in the required wavelength band. In order to adapt to specific environmental conditions, multiple filters for different bands are often loaded and linked to the camera via the 485 interface. To achieve switching.
Third, the development of optical fog technology because the direct use of light can penetrate the haze of the near-infrared wave band imaging, although the optical fog can only get black and white surveillance picture, but its imaging effect is prominent, but also in the maritime, the ocean has a good In recent years, large-scale projects such as safe cities and even the civilian market have also seen a large amount of fog demand.
At the same time, because the technology is relatively mature, you can consider loading two sets of lenses in a set of equipment, normally using a visible light lens, Fog is using a special fog lens, so that can retain the visible color of the screen, but also Can make the tolerance of the fog lens better, and achieve multi-screen contrast monitoring.
In practical applications, electron fogging, as an ISP image restoration technique, has a fatal flaw in that it cannot restore lost information when the fog is severe. This is determined by its imaging principle. Even if the image restoration algorithm is advanced, it cannot be improved. Once the concentration of haze in the environment changes, the effect of electron fogging will not be controllable. That is to say, the environmental adaptability of electronic fogging is weak, and the cost-effectiveness of developing more advanced image restoration algorithms is not high. Therefore, electronic fogging based on monitoring requirements is needed. Technology will gradually converge.
The large-scale optical fog monitoring camera system independently produced by our company has been applied in the fields of forest fire prevention, maritime affairs, and border defense. It has a long history of practical application, and its effect has also been recognized and recognized by users, with the development of new technologies. It is believed that the application prospects in various industries will become wider and wider. In addition to improving the optical fogging effect, in addition to the further enhancement of the camera's own image processing capabilities, the matching imaging systems such as lenses and windows should also have a higher level of infrared light. Transparency, therefore, upgrading and improving the supporting system is the direction of our company's future efforts in optical fogging.
