Development direction of video surveillance
現在のところ, there are various types of network surveillance cameras on the market. In terms of form, there are gun machine, ball machine, hemisphere machine, all-in-one machine, 等; In terms of functions, there are infrared, explosion-proof and perceptual cameras. However, as a security surveillance camera, the first requirement is to “see clearly”.
In recent years, with the increasing number of “Safe City” projects, the effect of low illumination of the camera at night has attracted more and more attention. Because of its excellent night imaging effect, it is widely used in “safe cities”, “safe villages and towns”, transportation, finance, high-end buildings, residential communities, campuses, ports and other application environments that require high low illuminance performance of cameras but are not suitable for additional light compensation equipment.
According to statistics, among all criminal cases, the night crime rate is as high as 74.4%. Bad conditions such as dim light and strong light in front of the car greatly interfere with the night monitoring effect and catalyze criminal acts. Whether the night picture is bright enough and can see the license plate clearly has become one of the most important indicators to judge the effect of a camera.
For night monitoring, infrared cameras, laser cameras and star level low illumination cameras are mainly used in the market at present. Infrared and laser cameras are cost-effective, but their defects are also obvious, such as high energy consumption, poor heat dissipation, small exposure range, and so on. したがって, the star level low illumination camera has gradually become the darling of the security market with its powerful night monitoring effect.
The ultra-low illumination camera usually refers to the camera with good sensitivity. It only needs a little light to present a brighter image.
Low illumination camera, mainly affected by lens, image sensor, back-end image processing technology and other factors, refers to a camera that can still obtain a relatively clear image under low illumination (i.e. low illumination). 現在のところ, the security industry usually divides the front-end camera into four levels. When the minimum illumination value reaches or even is lower than 0.0001Lux, it will reach the “star level” ultra-low illumination camera.
Illuminance: refers to the luminous flux of visible light received per unit area, usually in Lux. In the monitoring industry, the “lowest illuminance” value is usually used to indicate the sensitivity or sensitivity of the camera. In short, this value can be used to indicate how dark the camera can still see the available image. In a completely dark room, point the camera at the object to be measured, and then slowly dim the light until the object cannot be seen clearly on the display. At this time, the illuminance value displayed on the illuminometer is the lowest illuminance value of the camera.
They can be classified according to different illuminance values of cameras. The normal working illuminance range of the camera is divided into:
● Ordinary type, with the minimum illumination value between 0.1-1 ルクス;
● Moonlight type, with the minimum illumination value of about 0.01 ルクス;
● Starlight type, less than 0.001 ルクス.
Under the same lighting conditions, compared with the camera with normal illumination, the star level ultra-low illumination camera can present a brighter image.
In addition, if the minimum illuminance value of the camera is evaluated from the perspective of parameters rather than the effect, it also depends on the conditions under which the indicator is measured. Taking the gun type camera as an example, the complete expression of the minimum illumination value of the gun machine is usually: color 0.01Lux @ (F1.2, 50IRE, AGCON); Black and white 0.001Lux @ (F1.2, 50IRE, AGCON).
First, there are illuminance values in color mode and black and white mode. The camera sensitivity in black and white mode is higher, so the minimum illuminance is usually one order of magnitude lower than that in color mode;
Secondly, it is also necessary to pay attention to the F value of the lens used by the camera, the video signal measurement evaluation value, and the status of AGC. Only when these conditions are the same, it is meaningful to compare the low illumination values of two cameras;
Finally, it should be noted that when the infrared camera turns on the infrared light, it is generally considered that its illumination value is 0Lux.
Night monitoring cameras are mainly divided into three types: infrared cameras, thermal imaging cameras and ultra-low illumination cameras. These three types of cameras can be used in different monitoring environments due to their different imaging principles.
（1） Infrared camera
When the ambient light is dark to a certain extent, the infrared camera will automatically turn on its own infrared light. It will actively emit infrared light to illuminate the monitoring target, and then collect the reflected infrared light to generate an image. It is an active infrared. At this time, what we see is the image formed by infrared reflection, not the image formed by visible light reflection. In this way, we can take pictures of objects that cannot be seen by the naked eye in dark environments, that is, people often say that the illuminance value can reach 0 ルクス. したがって, if it is a relatively open environment, the infrared lamp has no reflective objects, so the image display effect will not be very good.
For infrared cameras, the life of infrared lamps is a common concern of users. The high temperature is one of the main factors leading to the failure of infrared lamps. Some studies show that the service life of infrared lamps can be extended by one year for every 10 ℃ temperature reduction. したがって, the heat dissipation design and power size of the infrared lamp circuit are very important, especially for long-distance infrared. The farther the distance is, the higher the power of the infrared lamp is, and the greater the heat will be. When the temperature is high to a certain extent, it will even affect the effect of the camera image sensor. This is the main problem of infrared camera.
（2） Thermal imaging camera
In nature, all substances above absolute zero (- 273 ℃) are constantly radiating electromagnetic waves related to their own properties and temperature. We call this phenomenon thermal radiation. At different temperatures, the wavelength of thermal radiation emitted by objects is different. The detection mechanism of thermal imaging camera is to use the infrared radiation characteristic image formed by the radiation difference between the target and the background or between various parts of the target to find and identify the target. Usually, it is made of high-purity germanium single crystal lens which is transparent to infrared light and does not penetrate visible light and ultraviolet light. At the same time, the thermal infrared detector is used to convert infrared radiation into electrical signals.
Because of the special working principle of thermal imaging camera, its imaging is not affected by light, and it is suitable for completely dark, strong light, backlight, glare and other environments. It can clearly distinguish different objects, and identify camouflaged and hidden targets. Compared with ordinary cameras, thermal imaging cameras have a longer detection distance. According to the different focal lengths of the selected lenses, the maximum monitoring distance can be several kilometers away. In addition, the thermal imaging camera can detect the infrared radiation of different wavelengths emitted by objects with different temperatures, so as to identify the temperature of the object surface. However, since it is necessary to absorb the energy radiated by the object before imaging, if there is a barrier between the monitored object and the camera, its imaging effect will be affected.
（3） Ultra low illumination camera
The ultra-low illumination camera usually refers to the camera with good sensitivity. It only needs a little light to present a brighter image. 現在のところ, the star level ultra-low illumination camera is the best type of camera in night monitoring. Because of its excellent night imaging effect, it is widely used in “safe cities”, “safe villages and towns”, transportation, finance, high-end buildings, residential communities, campuses, ports, high-speed highways, streets and other applications where the camera has high requirements for low illumination performance, but it is not suitable to add light compensation equipment. For example, in the scene of road monitoring to see the license plate, some city residents may feel that the addition of fill light will cause light pollution and reject the fill light equipment.
However, after the infrared camera illuminates the license plate, the special material of the license plate will cause reflection, so the details of the license plate cannot be seen clearly. したがって, if you want to see the license plate clearly, it is not suitable to use an infrared camera, and the star level ultra-low illumination camera appears, It immediately becomes a popular model in the “safe city” road monitoring. It can show bright images by using some weak street lights or ambient light to fill the light, so as to see the license plate clearly.
深セン金石康科技有限公司, 株式会社. focuses on the R&D, design, production and sales of camera modules. It has invested a lot of development and research work in face recognition technology, カメラ監視などの分野, and joined hands with its sister company, Shenzhen Jinchengtai Electronic Technology Co., 株式会社.
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