New concept: low illumination cameras lead night security

In recent years, with the development of CCD and DSP technology, low-light cameras have become mature and stable, and are used in many fields. However, industry experts believe that low-light cameras are not the mainstream of the market, and they are only used in some specific situations. If you add a light source that is costly or inconvenient to install a light source, a low-light camera can only function.

Low-illuminance cameras define the low-illuminance cameras currently on the market. Manufacturers or importers have different opinions about the definition of low-lightness. Color cameras are from 0.0004LUX to 1LUX, and black-and-white cameras are from 0.0003 to 0.1LUX. Infrared radiation can reach 0 LUX), which means that there is no uniform standard for the technical specifications of the CCTV industry in the domestic market. Industry insiders emphasize that the low illumination can not only depend on the aperture (F-number) of the lens, but also depends on the conditions under which the LUX value can be displayed. Otherwise, it is only a digital game! In terms of the aperture size (F value), the larger the aperture, the smaller the F value it represents and the lower the required illumination. In addition, does the electronic sensitivity (ELECTRONIC, SENSITIVITY) increase, and how many frames per frame are accumulated? Is infrared light ON or OFF? ... and so on should all be understood clearly and not confused by the illuminance values ​​indicated by the specifications. The evolution of low-light cameras in the Chinese market The development of low-light cameras in the Chinese market is simply divided into the following three steps: Day/night (COLOR/MONO), SLOW/SHUTTER, and EXVIEW/HAD. .

First, daytime color/night black and white (day/night camera COLOR/MONO)

This type of camera currently has its own specific demand group in the market. The COLOR/MONO camera's illuminance is even 0 LUX on the domestic market. We can't help but ask: “The camera is made of optical principles. How does it image at 0 illuminance?” Daytime color/night black and white (COLOR/MONO) The camera uses black-and-white images for high sensitivity to infrared rays. Under certain light conditions, the images are switched from color to black and white using line switching, which facilitates the use of infrared rays. In the course of the technological evolution of color/black and white line conversion, this kind of camera has adopted a single CCD (color) design, and is a color camera in daytime or when the light source is sufficient. When the night falls or the light source is insufficient (usually at 1 LUX to 3 LUX) The digital circuit eliminates color signals and turns them into black-and-white images. In order to match infrared rays, it also removes infrared filters that are indispensable for color cameras. The true “low-light camera” should refer to the camera itself (components, technologies used). The functions that can be achieved, while daytime color/night black and white cameras are limited by the CCD sensitivity, they cannot be changed by themselves. They only use line switching and infrared light to enhance the function and cannot be considered as a low light camera.

Second, slow shutter (SLOW / SHUTTER)

This type of camera is also known as a (screen) accumulation camera. It is a technique that uses computer memory to continuously accumulate several blurry pictures due to lack of light. It becomes a clear image and uses SLOWSHUTTER technology to reduce camera illumination. To 0.008 LUX/F1.2 (×128), and the number of frames the picture can accumulate (128 frames) is a leading level even within the imported brands. This type of low-light camera is suitable for museums that prohibit the destruction of red and ultraviolet rays, observation of biological activity at night, surveillance of military coastline during the night, and the monitoring of properties over static places.

Third, the degree of sensitivity camera (EXVIEW / HAD)

EXVIEW/HAD, also known as a 24-hour camera, has a color illuminance of up to 0.05 LUX and black and white up to 0.003 to 0.001 LUX (also with infrared to 0 LUX). It not only clearly discerns images, but also Real-time continuous picture.

Low-light camera technology The so-called low-light camera, that is, in the case of very low light, no other auxiliary light source can still identify the target object of the camera, common gun camera and dome camera.

Environmental illuminance (brightness) is usually measured in lux units. The smaller the value, the darker the environment. The illuminance index of the camera is also measured in lux. The smaller the value, the higher the sensitivity, and the more the objects in the dark can be seen. Therefore, the level of illumination becomes an important parameter for people to choose a camera.

Now, many manufacturers (businessmen) lower the camera's illuminance parameters from 1.0 lux to 0.1 lux to 0.001 lux. So, are these cameras really so sensitive? In order to truly understand the low-light camera, the following elaborates on two aspects.

CCD and supporting technology A complete camera equipment consists of two parts, the lens and the camera, and the camera is composed of a photosensitive device (CCD or CMOS, this article takes a CCD as an example), a complex signal processing circuit, and a filter.

The lens is an important part of the camera unit. Its function is to focus the light of the subject for the CCD of the camera, so that the scene is imaged on the CCD. The amount of light that can be captured directly determines the clarity of the CCD image. To measure how much light is taken by the lens, it is called the amount of light, and the amount of light entering the lens is expressed by the F value (aperture). F value = f (focal distance) / D (effective aperture of the lens), which is inversely proportional to the aperture, and is proportional to the distance from the focal point. With the same focal length, the larger the aperture of the lens, the smaller the F value and the greater the amount of light entering the lens. The F value of common lenses is mostly 1.2, 1.4, and there are currently F1.0 lenses. Therefore, in order to achieve the ideal low illumination effect of the camera, it is necessary to configure a lens that is suitable or configured with a small F value.

CCD photosensitive devices The current camera CCD is mainly used by three major suppliers, namely SONY, SHARP and LG, in these three kinds of CCD, SONY CCD sensitivity is relatively good, commonly used SONY CCD low illumination technology is Super HAD CCD; later SONY has also developed a super-sensitivity CCD, which SONY calls an EXPED CCD. The sensitivity of the CCD is 5 times that of a Super HAD CCD.

In addition, the size of the CCD also has a great impact on the sensitivity, the larger the size, the better the sensitivity. In order to make the camera have a lower illuminance index, 1/2-inch CCD cameras are often used. Data shows that the 1/3-inch CCD has only 56% of the 1/2-inch CCD, and the 1/4-inch CCD has only 44% of the 1/3-inch CCD.

The filter is a very small device of a color camera and plays an important role in the imaging effect of the camera. The filter removes infrared light. The CCD of the color camera can also sense infrared light, but because the infrared light can easily cause the DSP to calculate the correct color, it is necessary to add a filter to filter the light in the infrared light. Therefore, only the color CCD needs the filter, and the black and white CCD does not installation.

In order to obtain lower illuminance, low-light cameras need to take in some infrared light in addition to the visible light, and infrared light of different wavelengths will be ingested and will have a certain impact on the imaging of the camera. Therefore, it is necessary to filter out unwanted light. Infrared light while retaining the necessary infrared light filter. At present, high-end low-light cameras use dual filters, that is, non-inductive infrared filters are used during the day to obtain clear images, and infrared-sensitive filters are used at night to obtain lower illumination. This type of camera will have a photo-resistor. When the photo-resistor senses that the ambient light is insufficient, the trigger circuit in the camera will be activated, and the filter that does not induce infrared light will be switched to the filter that senses infrared light. The higher-end camera switches to a black and white image while switching filters, which results in better image quality. Of course, during the conversion process, you will encounter a critical value problem. If the light just switches back and forth when it is set to a critical value, it will not only affect the imaging effect, but also affect the life of the filter due to non-stop mechanical motion. Therefore, some manufacturers add a delay circuit in the camera, that is, when the critical value is reached, the delay is switched for a period of time. If the illumination continues to decrease during this period, the switching is performed. If the delay remains unchanged or increases, the switching is not performed. .

Image DSP processing low-light camera development so far, not only the development of hardware technology, but also outstanding performance for DSP image processing, such as color to black technology and low-speed electronic shutter, the emergence of the frame accumulation technology.

The color to black technology usually black and white camera's sensitivity is much higher than the color camera's sensitivity, because the black and white camera, DSP operation only handles two colors, namely black and white, so now a considerable part of the low-light camera has a color The black-and-white function, that is, the daytime color image, is converted into a black-and-white image by software processing at night, and a lower illumination is obtained by sacrificing the color effect.

The process of converting color to black and white is controlled by the charge converted by the CCD to collect light. When the charge intensity reaches a certain critical value, it is automatically converted to a black and white image. Similarly, in order to ensure that the critical value will not cause repeated switching, it will do A delay in processing.

Low-speed electronic shutter technology The low-speed electronic shutter utilizes the technology of computer memory to successively stack several pictures that are blurred due to insufficient light, and become a relatively clear picture. In the CCD camera, the shutter is operated by the charge accumulation time of the surface of the optically-controlled image, and the electronic shutter controls the accumulation time of the camera CCD. When the speed of the electronic shutter increases, the CCD is focused on within the permissible time of each video field. The reduction in light will reduce the camera's sensitivity. The ordinary camera's electronic shutter is PAL: 1/50-1/100000 seconds, NTSC is 1/60-1/100000 seconds, the low-speed electronic shutter can slow down the exposure speed of the shutter, making the CCD can accumulate charge for a longer time and thus low Under the illumination environment, a relatively clear picture is obtained. Now the frame-accumulating camera slows down its low-speed electronic shutter by up to 128 times that of a normal camera. However, with the slowing down of the electronic shutter speed, the camera image tailing phenomenon will occur. Such cameras are more suitable for the monitoring of still pictures, and it is not suitable to use vigorously moving picture monitoring.

Through the above analysis, the user can not blindly look at the minimum illuminance parameters marked by each merchant when selecting a low-light camera, but should select the corresponding low-illuminance camera according to the application environment, requirements, monitoring objects, and economic capabilities. If you choose 1/2 inch or 1/3 inch camera; choose Super HAD CCD technology or choose EXview HAD CCD technology or frame accumulation technology; also consider whether to have color to black and white function, whether to use a dual filter switch Technology and so on.

Of course, any low-light camera needs a certain amount of light to be used. As for the degree of illumination, it involves the sensitivity of a low-light camera. So there is no 0LUX camera. The so-called OLUX means there is no visible light. This requires the infrared light to make up for the camera to work. However, in some places, infrared cameras have been banned from use, so so far, low-light cameras still have an irreplaceable position. If the museum prohibits infrared ultraviolet rays, and these sites must be monitored for 24 hours, it is recommended for the most demanding applications that the CCD-size cameras such as 1/2-inch cameras should be selected as much as possible. In some flammable and explosive warehouses and coal mines, infrared cameras have a large amount of heat, which may cause spontaneous combustion and cause fires. Infrared cameras are also prohibited at these sites; there are military coastlines and other places, due to the wavelength emitted by infrared cameras. It is easily forbidden by some special instruments. Only low-light cameras can be selected.

Low-illuminance camera application The current focus of low-light cameras for road monitoring is the highway toll monitoring system, which is mainly for the toll stations' toll lanes, toll plazas, and toll booths, the types of vehicles that the toll lanes pass, and the toll collectors’ Observe and record emergencies and special events in the operation process and charging process, and implement effective supervision. Especially at night, toll booth staff need to see the license plate. Under normal circumstances, after the lights are turned on, the ambient illumination and the license plate illumination on the road form a certain dynamic range. Traditional cameras are difficult to “see”, so they are low. Illumination cameras have a great demand.

Followed by the electronic police system, through closed-circuit television monitoring and red light automatic video recording and other means to improve the command center's intuitive, real-time mobility and ability to respond to traffic accidents and accidents, as well as enhance investigation and punishment of the objectivity of the violation, and Full coordination and control of the control area to improve the traffic capacity of the vehicle. Due to the need to see the license plate, 24-hour monitoring, so there is a demand for low-light cameras.

In addition to some of the more traditional monitoring areas, there may be situations where it may be inconvenient to add light sources in a low-light environment. For example, in a hospital ward, it is desirable to perform performance assessments for doctors or on-duty nurses. If a light source is added to the ward, it will affect the patient's rest. Therefore, a low-light camera is needed. There are also places where light sources are not suitable. Special units such as prisons need to install cameras in concealed locations.

Currently, the application of low-light cameras is not limited to the monitoring of CCTV applications, including some equipment manufacturing industry, biomedical and military research and other fields have a wide range of applications, such as the ultimate ultra-illuminance camera Samsung Photoelectron Research, the illuminance value Can reach 0.000008Lux, this product is mainly used in the field of medical applications requiring high-definition. In addition, in some areas in addition to the concern about the characteristics of the product indicators, the product's external dimensions have also been considered to the extent of care. The development of low-light cameras requires not only focusing on the needs of the current monitoring field, but also listening to the needs of other industries to solve low-light conditions to obtain low-noise images. In addition, the corresponding spectrum of spectrum can be made wider to accommodate more The needs of the field.