The main body of the camera part is video camera Its function is to observe and collect information. The performance of the camera and its installation mode are important factors that determine the quality of the system. The following parameters should be noted when selecting a surveillance camera:
1) Color: There are black and white cameras and color cameras. Generally, the horizontal definition of black and white cameras is higher than that of color cameras, and black and white cameras are more sensitive than color cameras. They are more suitable for places with insufficient light and places with dark lights at night. Black and white cameras are cheaper than color cameras. However, the color image is easy to distinguish the color of clothes and scenes, which is convenient to obtain and distinguish the real-time information of the scene in time.
2) Definition: There are two kinds of definition: horizontal definition and vertical definition. The definition in the vertical direction is limited by the TV system, which has a maximum limit. Since all TV signals in China are PAL system, the vertical definition of PAL system is 400 lines. Therefore, the camera definition is generally expressed in horizontal definition. Horizontal definition refers to the measurement of the human eye on the horizontal detail definition of the TV image, which is expressed by TV line TVL.
At present, the horizontal definition of black and white cameras should be more than 500 lines, and that of color cameras should be more than 400 lines.
3) Illuminance: The luminous flux received per unit illuminated area is called illuminance. Lux is the illuminance when the beam of nominal brightness (lumen) evenly shines on the area of lm2. The sensitivity of the camera is expressed by the lowest illuminance, which means that the camera uses a specific test card as the uptake target. When the lens aperture is 0.4, adjust the illuminance of the light source, and use an oscilloscope to measure the video signal amplitude at its output end to be 10% of the rated value. At this time, the measured illuminance of the test card is the lowest illuminance of the camera. So in fact, the illuminance of the subject should be about 10 times more than the minimum illuminance to obtain a clearer image.
At present, the minimum illuminance of black and white cameras is generally selected. When the relative aperture is F ／ 1.4, the minimum illuminance is required to be less than 0.1Lux; The minimum illuminance of color camera shall be selected. When the relative aperture is F ／ 1.4, the minimum illuminance shall be less than 0.2Lux.
4) Synchronization: the camera is required to have power synchronization and external synchronization signal interfaces. For power synchronization, all cameras are powered by the AC in-phase power supply of the monitoring center, so as to lock the phase of the camera airport synchronization signal and the city power supply, so as to achieve the synchronization mode of camera synchronization signal phase consistency.
In terms of external synchronization, it is required to configure a synchronous signal generator to realize forced synchronization. The working mode of the line frequency, field frequency, frame rate signals used for the TV system scanning, and the composite blanking signal is synchronized with the synchronous signal provided by the peripheral signal generator.
Only when the system is synchronized, the image will not roll when timing switching, and the quality of recording and playing can be improved.
5) Power supply: generally, the camera power supply includes AC 220V, AC 24V, DC 12V. The camera power supply can be selected according to the site conditions, but it is recommended to use safe low voltage. When 12V DC voltage is selected for power supply, it often fails to meet the requirements of camera power synchronization. External synchronization must be adopted to achieve the purpose of system synchronous switching.
6) Automatic gain control (AGC): In the case of low brightness, the automatic gain function can improve the intensity of the image signal to obtain a clear image. At present, the minimum illuminance of CCD camera on the market is the parameter under this condition.
7) Automatic white balance: When the white balance of the color camera is normal, the color of the subject can be truly restored. The automatic white balance of color camera is to realize its automatic adjustment.
8) Electronic brightness control: some CCD cameras can adjust the exposure time of the CCD image sensor by using the electronic shutter according to the brightness of the incoming light, so that the automatic aperture lens can not be used when the light changes greatly. When using the electronic brightness control, the depth of field of the subject is smaller than when using the automatic aperture lens.
9) Backlight compensation
