Ultra-low-light cameras are hot spot products in the surveillance industry that have been launched in recent years with the development of semiconductor technology. It has been widely used in the fields of finance, cultural museums, hotels, office buildings, and property management in residential quarters. Since traditional cameras cannot meet the demand for continuous 24-hour surveillance (because it is impossible to turn on the lights 24 hours in any location), new technology-based ultra-low-light cameras have seized this opportunity and developed rapidly.
General ultra-low-light cameras mostly adopt exview had technology. The sensitivity to external light of cameras that adopt exview had ccd will be greatly increased. In the near-infrared region, the sensitivity can be increased to 4 times that of ordinary cameras, such as (Figure 1). Therefore, even in a very dark environment, this camera can usually see objects invisible to the human eye. The emergence of this technology is welcomed by the surveillance market, and the camera can achieve the best effects in various lighting environments. Especially when it is matched with special infrared lighting equipment, high-definition black-and-white images can be obtained, and 0-illuminance monitoring can be achieved (in the case of completely no light). In the near-infrared region of 760mm-1100mm, if it is combined with infrared illumination with the appropriate wavelength, clear black and white images can be achieved.
Similarly, the method of obtaining images under low illuminance is to increase the amount of exposure of the ccd in a single frame of image by accumulating a single frame of charge, thereby increasing the sensitivity of the camera to a single frame of image. This method can also obtain low illuminance indicators, but the cost is the coherence of the image will be reduced, so when choosing this camera, be careful not to use it with the PTZ as much as possible, otherwise it will give rise to the phenomenon of losing the picture. There are some other methods for obtaining images under low illuminance, but none of them can fundamentally solve the illuminance problem.
In addition, there are several points to note when choosing to use low-light cameras and infrared lamps.
First, the appropriate lens must be selected. In order to improve the camera's sensitivity to infrared lights and scenes, a lens with a large luminous flux should be used as much as possible, and attention should be paid to increasing the drive level value of the aperture as much as possible when using an automatic diaphragm or a motorized two-variable lens. Generally, as the focal length of the lens increases, the luminous flux will be relatively reduced. When choosing an infrared lamp, you must leave a certain margin and pay attention to the nominal index of the infrared lamp.
Second, the optional power supply of the infrared lamp should meet the minimum electric power required by it as much as possible. The situation that irradiation distance is insufficient occurs frequently.
Third, consider the degree of reflection of the photographed scene. Since infrared has the same characteristics as visible light, such as reflection and refraction, the distance margin should be considered if there is no good reflective environment (such as buildings, walls, signs) around the target scene.
At present, in terms of the low-light cameras advertised on the market, both manufacturers and importers have different opinions on the definition of low-light. There is no agreement. Color cameras range from 0.0004 lux to 1 lux, and black and white cameras range from 0.0003 to 0.1 lux. (If they are matched with infrared, they can both reach 0lux). This is the case that there is no uniform standard for the technical specifications of the cctv industry in the domestic market, and each manufacturers has its own words.
People in the industry emphasize that how low the illuminance can be depends not only on the aperture size (f value) of the lens, but also on the conditions under which the marked lux value can appear, otherwise it is just a game of numbers! In terms of aperture size (f value), the larger the aperture, the smaller the f value it represents, and the lower the required illuminance. In addition, customers should understand clearly issues such as is the electronic sensitivity improved; what is the cumulative frame number of a single screen; is infrared on or off..., so as not to be confused by the illuminance value indicated in the specification. The evolution of low-light cameras in the Chinese market is simply divided into the following three steps: daytime color/night black and white (color/mono); low-speed shutter (slow/shutter) and super sensitivity cameras (exview/had).
1. Daytime color/night black and white (day and night camera color/mono)
There are still groups of people with demands for such cameras in the market. The lowest marked value of illuminance of day and night (color/mono) cameras is even 0lux in the domestic market. We cannot help asking: "The camera is made according to optical principles. How can imaging be made at 0 illuminance?"
The daytime color/night black and white (color/mono) camera uses the characteristic that black and white images have high sensitivity to infrared rays. Under certain light source conditions, the image is switched from color to black and white by means of circuit switching to facilitate the matching with infrared rays. In the process of technological evolution of color/black and white circuit switching, this type of camera has adopted a single ccd (color) design, which means it is a color camera during the day or when the light source is sufficient, and when the night falls or the light source is insufficient (usually 1lux to 3lux), the color signal is eliminated by the digital circuit and images become black-and-white. Besides, in order to match the infrared, the indispensable infrared filter of the color camera is also removed. The real "low-light camera" should refer to the achievable functions of camera itself (the components and technology used), while daytime color/night black and white camera itself cannot be changed due to the limitation of ccd sensitivity. It only uses circuit switching and infrared light to improve the functions, which can not be regarded as low-light cameras.
This type of camera is also called (picture) accumulation camera. It uses computer memory technology to continuously accumulate several blurry pictures due to insufficient light to form a clear picture. Slow shutter technology is used to lower the the illuminance of camera to 0.008lux/f1.2 (×128), and its number of frames that can be accumulated (128 frames) is at the leading level even when it is competed with imported brands. This type of low-light camera is suitable for museums that prohibit red and ultraviolet damage, observation of biological activities at night, surveillance of military coastlines at night, and the surveillance of places with relatively static properties.
3. Super sensitivity camera (exview/had)
The super sensitivity camera (exview/had), also known as the 24-hour camera, has a color illuminance of up to 0.05 lux, and a black and white illuminance of up to 0.003 to 0.001 lux (it can also be used with infrared to reach 0 lux), which not only can clearly identify the image, but also record real-time continuous pictures.