One, the parameters of the light-sensitive components
At present, the mainstream surveillance camera light-sensitive components using CCD components, in fact, is the photoelectric conversion element. Compared with the previous CMOS sensor, CCD sensitivity is CMOS 3 to 10 times, so the CCD chip can receive more light signals, converted to electrical signals, filtered by the video processing circuit, amplified to form a video signal output. The stronger the light signal received, the greater the amplitude of the video signal. The video signal is connected to the video input of the monitor or television can see the video image. Improve the clarity of the image is fundamental to improve the camera's light-sensitive capabilities.
Two, the parameters of the lens
Aperture: aperture mounted on the back of the lens, the larger the aperture opening, the greater the amount of light through the lens, the higher the clarity of the image; aperture opening the smaller, the smaller the amount of light through the lens, the lower the clarity of the image. Usually expressed in F (luminous flux), F = focal length (f) / through the light aperture. In the technical specifications of the camera, we can often see 6mm/F1.4 such a parameter, which indicates that the focal length of the lens is 6mm, the luminous flux is 1.4, then we can easily calculate the through-light aperture of 4.29mm. in the case of the focal length f the same, the smaller the value of F, the larger the aperture, the luminous flux to reach the CCD chip is the bigger the lens is better.
Field of view: In engineering practice, we often use the horizontal field of view to reflect the shooting range of the screen. The larger the focal length f, the smaller the field of view angle, the smaller the range of the picture formed on the sensor; conversely, the smaller the focal length f, the larger the field of view angle, the larger the range of the picture formed on the sensor.
Focal length (f): the focal length is the distance between the lens and the photographic element, by changing the focal length of the lens, you can change the magnification of the lens, changing the size of the captured image. When the distance between the object and the lens is very far, we can use the following formula: lens magnification ≈ focal length / object distance. Increase the focal length of the lens, the magnification increases, you can bring the distant scene closer, the scope of the picture is small, the details of the distant scene to see more clearly; if you reduce the focal length of the lens, the magnification is reduced, the scope of the picture is expanded to see a larger scene.
Surveillance camera pixels and resolution than the computer video head to be high but can not catch up with the professional digital camera or dv. Surveillance camera is just a single video capture device, does not have the data preservation function.
Three, how to capture a clear image in poor lighting conditions
Surveillance cameras require poor lighting conditions at night or even no light in the environment, but also to capture a clear image. In the camera's indicators, we can often see the low illumination of this item.
Four, the control of the camera
In order to expand the scope of monitoring, the requirements of the surveillance camera can realize the rotation, zoom, zoom magnification, auto-focus and so on. The realization of these functions, the need for digital hard disk recorders through the controller to control the camera.
1, rotary control
Engineers use the head to install and fix the camera, the head is divided into fixed head and motorized head. Fixed head is suitable for monitoring the scope of the situation is not large, in the fixed head after the installation of the camera, adjust the camera level and tilt angle, to achieve the best working condition after locking the adjustment mechanism can be. Motorized PTZ installed stepping motor, the motor accepts signals from the controller, driving the camera to rotate to achieve precise positioning, suitable for a wide range of monitoring.
The PTZ can be divided into horizontal rotary PTZ which can only rotate left and right, and omni-directional PTZ which can rotate left and right as well as up and down according to its rotary characteristics. Generally speaking, the horizontal rotation angle of 0 ° ~ 350 °, vertical rotation angle of +90 °. The horizontal rotation speed of the constant speed gimbal is generally 3° to 10°/s, and the vertical speed is about 4°/s. The horizontal rotation speed of the variable speed gimbal is 0° to 350°, and the vertical rotation angle is +90°. The horizontal rotation speed of the variable speed head is generally in the range of 0° to 32°/s, and the vertical rotation speed is around 0° to 16°/s. In some high-speed camera systems, the horizontal rotation speed of the head is as high as 480°/s or more, and the vertical rotation speed is 120°/s or more.
2, the realization of motorized zoom, zoom, auto-focus
(1) the so-called integrated camera is to make the lens, CCD chip, video processing circuitry, power supply, housing integration as a whole, can realize the motorized zoom, zoom, auto-focus function. Can quickly and accurately realize the auto-focus is the key to evaluate the quality of integrated cameras. Good products can be accurately focused at once, while the poor quality of the product, the focus will be back and forth, the need for many times to focus. The current integrated camera to 16, 18, 20, 22, 27, 32 times zoom as the mainstream, the development trend is that the illumination is getting lower and lower, the optical multiplier is getting higher and higher. Note that the zoom multiplier here refers to the optical zoom.
The key technology of integrated camera is lens, CCD and DSP processing module. High-grade lenses are mainly mastered by Japanese manufacturers, such as Canon, Camputar, Avenir, etc. CCD chip to Japan Sony-based, Sony CCD is divided into SuperHAD and Exview two types, of which Exview is the latest technology, generally 1/4 inch size, sex-to-noise ratio higher than SuperHAD; in the DSP processing chips On the DSP processing chip, Sony's DSP chip can be very good image color processing, so that the image looks very bright. The DSP of Canon and Nikon is better in light capture mode and focusing.
(2) the use of motorized zoom lens + ordinary video camera to combine the motorized zoom lens and ordinary video camera, the use of ordinary video camera video drive principle, to achieve automatic control of the lens focal length, aperture, focus. Some manufacturers have developed an ultra-high-magnification 60 times electric zoom lens "D60 × 12.5". Its 750mm (up to 1500mm when using zoom extension lens) focal length can distinctly identify the characters 3 kilometers away.
V. Network transmission of video images
1, analog camera + digital hard disk recorder + computer network system
This is the most widely used network video surveillance system, through the setting of ports, gateways and routing, the site of the digital hard disk recorder as a server, in the remote customer's computer to install special monitoring software or plug-ins, the user will be able to Through the Internet to see thousands of miles away from the scene, to achieve single-channel, multi-channel video remote monitoring and recording.
2, analog camera + network video server + computer network system
Analog camera output signal is an analog signal, the computer processes the signal is a digital signal, in the network transmission of digital signals, network video servers (VideoServer) to the analog camera's analog signals converted to digital signals, and then through the high-efficiency compression chips, compression, encoding, the output can be in the computer. Network Video Server (VideoServer) converts analog signals from analog cameras into digital signals, and then after efficient compression chip compression, encoding, the output can be transmitted in the computer network of digital signals, digital signals transmitted in the form of computer networks. Therefore, the network video server can also be called a video encoder (VideoCoder). When one end of the video server is connected to the output signal of the analog camera, the other end is plugged into the computer network cable, and then set up the gateway and route in any computer in the Internet, open IE browser, enter the IP address or domain name to see the monitoring screen in the computer. If the analog camera is equipped with a PTZ, we can also control the camera through the computer to zoom, zoom, rotate and other control operations. In the network video server must also be embedded in the real-time operating system, can be a Linux version, or Windows version, from the stability of the Linux version is better. The use of network video servers can be selected and equipped with different cameras, with more flexibility.
3, network camera + computer network system
Network camera is the analog camera and network video server integrated together. Built-in analog/digital conversion inside the camera, video server functions, and network video server, according to network protocols to achieve network communication and data transmission, but also to receive alarm signals and send alarm signals to the outside. This is more convenient, as long as the network camera is installed, plug in the Internet cable can be browsed.
4, CDMA wireless network video surveillance system
The transmission described above is wired transmission, but in the mobile transportation (car), remote mines, mountainous areas, the use of wired transmission is obviously very difficult, we can use the mature wireless communication technology. The representative products here are China Unicom's MobileVision. The CDMA wireless network video surveillance system is a convenient product that integrates CDMA data communication function and digital video coding function into one. It compresses the camera image through the video compression and coding module and transmits it to the CDMA network through the intelligent wireless communication terminal to realize the functions of video data interaction, sending/receiving, encryption/decryption, coding/decoding, and link control and maintenance, etc. The system can transmit real-time moving images to the CDMA network. The system can transmit real-time moving images to the nearest Unicom communication network. Real-time image information can be obtained from the central control terminal of the system through the Internet. The system integrates the advantages of CDMA network and Internet network to carry out remote monitoring and management anytime and anywhere.
Six, commonly used technical indicators explained
1, resolution
Image resolution simply refers to the number of points displayed on the screen horizontally and vertically in the direction. For example, 1024 × 728, of which "1024" represents the number of points displayed on the screen in the horizontal direction, "768" represents the number of points displayed in the vertical direction. The higher the resolution, the clearer the image. The higher the resolution, the clearer the image display.
2, clarity
The clarity of the camera with a line, divided into horizontal and vertical lines, in the actual engineering applications, we often use the horizontal line as an assessment of the clarity of the camera indicators, the more the number of lines, the higher the clarity. Commonly used black-and-white camera clarity is generally 450-600, while the clarity of the color camera is generally 330-480, the larger the value of the image is clearer. General surveillance occasions, with about 450 lines of the camera can meet the requirements, for medical, image processing and other special occasions, with 600 lines of the camera can get a clearer image.
3, automatic gain control (AGC)
In order to enable the camera to output standard video signals in different illumination conditions, the introduction of automatic gain control in the video processing circuit (AutoGainControl), by detecting the average level of the video signal to achieve gain feedback control. Cameras with AGC function have improved sensitivity at low illumination, but also amplify the interference signal, making the image look cluttered.
4, backlight compensation (BLC)
When the camera is in a backlight environment, the picture will appear black image, however, in the security backlight environment is difficult to avoid, this time the need for backlight compensation. When the introduction of backlight compensation function, the camera if the video level detected in a region of the shooting image is relatively low, through the AGC circuit described above to improve and enhance the video level of the region, to improve the amplitude of the output video signal, so that the image as a whole clear and bright. If the subject you want to see appears dark due to the bright background, you can set the BLC to ON, thus compensating for the strong backlight.
5, electronic shutter (EE/AI) switch
In the rear terminal of the smart camera we can often see the EE/AI switch switch. EE means electronic shutter mode; AI means automatic aperture lens mode. The camera's electronic shutter is generally set to automatic electronic shutter mode, through the electronic shutter mode, according to the intensity of the incident light to adjust the exposure time of the CCD image sensor, so as to get a clear image, the electronic shutter time between 1/50-1/100000 seconds.
6, signal-to-noise ratio
The ratio of signal level to clutter level, clutter, including power clutter, random clutter, single-frequency clutter. Often expressed in decibels (dB). The higher the signal-to-noise ratio indicates that it produces less clutter, the higher the quality of the image signal. Signal-to-noise ratio shall not be less than 48dB.
7, white balance (AWB)
Color camera to restore the color of the object being photographed, you must maintain a normal white balance.
Surveillance camera parameters how to see
IRLED said infrared lamps. IRLED: 25 * 6PCS + 8 * 6PCS said the number of infrared lamps is also the configuration of the lens is six or eight lamps.
PCS means "Piece", 25*6PCS means that there are 6 pieces of IR LEDs with a diameter of 25mm.
IRLEDWorkingDistance: the furthest working distance of infrared.
Because infrared lamps are generally dispersed irradiation, so far enough away from the place can not converge, so that the function of infrared irradiation can not be played, the general power of small infrared lamps basically in the working distance of about 50 meters, the power of the large 100 surface.
IRLEDWorkingDistance:100m, meaning that the camera's normal infrared light can hit a distance of 100 meters, and through the camera can be viewed without visible light within the range of 100.
Lens: means the lens length, long distance camera, lens is relatively large.
Image SensorLmageSensorSHARP/SONY: This is the chip of the surveillance camera.