Teach you how to choose a surveillance camera
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1) Color: The camera has two kinds of black and white and color, usually the horizontal resolution of the black and white camera is higher than that of the color camera, and the black and white camera is more sensitive than the color camera, and is more suitable for places with insufficient light and places with dark night lights. Black and white cameras are cheaper than color. However, colored images can easily distinguish the colors of clothes and scenes, which facilitates the timely acquisition and differentiation of real-time information at the scene.
2) Sharpness: There are two kinds of horizontal resolution and vertical resolution. The definition of the vertical direction is limited by the television system and has the highest limit. Since the television signal in our country is PAL format, the vertical resolution of PAL system is 400 lines. So the definition of the camera is usually expressed in horizontal resolution. Horizontal resolution represents a measure of the level of detail sharpness of the human eye to the television image, represented by the television line TVL.
At present, the horizontal resolution of a black-and-white camera is generally required to be greater than 500 lines, and the horizontal resolution of a color camera is generally required to be greater than 400 lines.
3) Illuminance: The luminous flux received on the illuminated area is called illuminance. Lux is the illuminance of a light beam with a nominal luminous intensity (lumens) uniformly projected on an lm2 area. The sensitivity of the camera is represented by the minimum illuminance. This is a camera that uses a specific test card as the ingestion target. When the lens aperture is 0.4, the illuminance of the light source is adjusted, and the amplitude of the video signal at the output end is measured with an oscilloscope to be 10% of the rated value. The measured test card illumination is the minimum illumination of the camera. Therefore, the illuminance of the subject should be approximately 10 times more than the minimum illuminance to obtain a clearer image.
At present, the minimum illuminance of the black and white camera is generally selected. When the relative aperture is F/1.4, the minimum illuminance requirement is less than 0.1 Lux; if the minimum illuminance of the color camera is selected, when the relative aperture is F/1.4, the minimum illuminance requirement is less than 0.2 Lux.
4) Synchronization: The camera is required to have a power synchronization and external synchronization signal interface. For power synchronization, all cameras are powered by the AC in-phase power supply of the monitoring center, which locks the phase of the camera's field synchronization signal with the mains to achieve the same phase synchronization of the camera's synchronization signal.
For external synchronization, a synchronous signal generator is required to implement forced synchronization, the line frequency, field frequency, and frame frequency signals used by the television system for scanning, and the synchronization between the composite blanking signal and the synchronization signal provided by the peripheral signal generator. the way.
Only in the case of synchronization, the system will not appear scrolling when the images are switched, and recording and playback quality can be improved.
5) Power supply: The camera power supply generally has an AC 220V, AC 24V, and DC 12V. The camera power can be selected according to site conditions, but safe low voltage is recommended. When the 12V DC voltage is used for power supply, the synchronization of the camera power supply is often not achieved, and external synchronization must be used to achieve the purpose of system synchronous switching.
6) Automatic gain control (AGC): In the case of low brightness, the automatic gain function can increase the intensity of the image signal to obtain a clear image. At present, the minimum illuminance of CCD cameras on the market is a parameter under this condition.
7) Auto 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 the color camera is to achieve its automatic adjustment.
8) Electronic brightness control: Some CCD cameras can use the electronic shutter to adjust the exposure time of the CCD image sensor according to the brightness of the incident light, so that the automatic iris lens can be used when the light changes greatly. With electronic brightness control, the depth of field of the subject is smaller than when using an auto iris lens.
9) Backlight compensation: In the case where only the backlight is installed, when the ordinary camera is used, the image of the subject will be black, and a camera with backlight compensation should be used to obtain a clearer image.