Buy a high-definition surveillance camera to see what parameters.

The function of the monitoring camera is to take pictures of the monitoring area and convert them into electrical signals. According to the specifications, it can be divided into 1/3 ",1/2" and 2/3 ",and the installation methods are fixed and desktop with cloud. When buying this kind of security products, we should pay attention to its parameters, so what parameters should we look at when buying a high-definition surveillance camera? Parameters of photosensitive element, parameters of lens, control of camera, network transmission of video image, resolution, clarity and so on. The following introduces some problems that should be paid attention to when purchasing monitoring camera parameters. Parameter interpretation of high-definition surveillance camera

First, the parameters of the photosensitive element

At present, the photosensitive elements of mainstream surveillance cameras all use CCD elements, which are actually photoelectric conversion elements. Compared with the previous CMOS photosensitive elements, the sensitivity of CCD is 3 to 10 times that of CMOS, so the CCD chip can receive more optical signals, which are converted into electrical signals by video processing circuits, filtered and amplified to form video signals for output. The stronger the received optical signal, the greater the amplitude of the video signal. When the video signal is connected to the video input of the monitor or TV, you can see the video image. The fundamental thing to improve the image definition is to improve the sensitivity of the camera.

Second, the parameters of the lens

Aperture: The aperture is installed behind the lens. The larger the aperture, the greater the amount of light passing through the lens and the higher the definition of the image. The smaller the aperture, the less light passes through the lens and the lower the definition of the image. It is usually expressed by F (luminous flux). F= focal length (f)/ aperture. In the technical indicators of the camera, we can often see such parameters as 6mm/F 1.4, that is to say, the focal length of the lens is 6mm and the luminous flux is 1.4. At this time, we can easily calculate that the aperture is 4.29 mm. Under the same focal length f, the smaller the f value, the larger the aperture, the greater the luminous flux reaching the CCD chip and the better the lens.

Perspective: In engineering practice, we often use horizontal perspective to reflect the shooting range of the picture. The larger the focal length f, the smaller the field of view angle, and the smaller the picture range formed on the photosensitive element; Conversely, the smaller the focal length f, the larger the field of view angle and the larger the picture range formed on the photosensitive element.

Focal length (f): The focal length is the distance between the lens and the photosensitive element. By changing the focal length of the lens, the magnification of the lens can be changed and the size of the shot image can be changed. When the object is far away from the lens, we can use the following formula: the magnification of the lens ≈ focal length/object distance. By increasing the focal length and magnification of the lens, the foreground can be narrowed, the picture range is smaller and the foreground details can be seen more clearly; If the focal length of the lens is reduced, the magnification is reduced and the picture range is expanded, a larger scene can be seen.

The pixel and resolution of surveillance camera are higher than that of computer video head, but it can't catch up with professional digital camera or dv. The surveillance camera is just a single video acquisition device with no data storage function.

Third, how to shoot a clear image in poor light?

It is required that the surveillance camera can capture clear images in poor lighting conditions or even in the dark environment at night. In the indicator of the camera, we can often see items with low illumination.

Fourth, camera control.

In order to expand the monitoring range, it is required that the monitoring camera can realize the functions of rotation, zoom, zoom and autofocus. The realization of these functions requires the digital hard disk video recorder to control the camera through the controller.

1, rotation control

Engineers use pan/tilt to install and fix cameras. Pan-tilt is divided into fixed pan-tilt and electric pan-tilt Fixed pan/tilt is suitable for occasions with small monitoring range. After installing the camera on the fixed pan/tilt, adjust the horizontal and pitching angles of the camera, and lock the adjustment mechanism after reaching the best working state. The electric pan/tilt is equipped with a stepping motor, which receives the signal from the controller and drives the camera to rotate, thus realizing accurate positioning and being suitable for large-scale monitoring.

According to the rotation characteristics of the tripod head, the tripod head can be divided into a horizontal tripod head that can only rotate left and right and an omnidirectional tripod head that can rotate left and right and up and down. Generally speaking, the horizontal rotation angle is 0 ~ 350 and the vertical rotation angle is+90. The horizontal rotation speed of constant-speed pan-tilt is generally 3 ~ 10/s and the vertical speed is about 4 /s s. The horizontal rotation speed of variable-speed pan-tilt is generally 0 ~ 32/s and the vertical rotation speed is about 0 ~16/s. In some high-speed camera systems, the horizontal rotation speed of pan-tilt is above 480/s and vertical. ..

2. Realize electric zoom, zoom and autofocus.

(1) The so-called integrated camera integrates the lens, CCD chip, video processing circuit, power supply and housing, and can realize electric zoom, zoom, autofocus and other functions. Whether autofocus can be realized quickly and accurately is the key to evaluate the quality of integrated camera. A good product can focus accurately at one time, while a poor product will go back and forth when focusing, and it needs to set the focus several times. At present, the mainstream of integrated cameras is the magnification of 16, 18, 20, 22, 27 and 32, and the development trend is lower and lower illumination and higher optical magnification. Note that the zoom magnification here refers to the optical zoom magnification.

The key technologies of integrated camera are lens, CCD and DSP processing module. High-end lenses are mainly controlled by Japanese manufacturers, such as Canon, Camputar and Avenir. The CCD chip is mainly Sony of Japan, and SonyCCD can be divided into SuperHAD and Exview, among which Exview is the latest technology, generally adopting the size of 1/4 inches, and the SNR is higher than Super HAD. On the DSP processing chip, Sony's DSP chip can handle the image color very well, making the image look very bright. The DSP of Canon and Nikon is better in grasping light mode and focusing.

(2) The electric zoom lens is combined with the common camera, and the automatic control of lens focal length, aperture and focusing is realized by using the video driving principle of the common camera. At present, manufacturers have developed the ultra-high magnification 60x electric zoom lens "D60× 12.5". Its focal length of 750mm (up to 1500mm when using a zoom lens) can clearly identify people 3 kilometers away.

Verb (abbreviation of verb) video image network transmission

1, analog camera+digital hard disk video recorder+computer network system

This is the most widely used network video monitoring system at present. By setting ports, gateways and routes, using digital hard disk video recorders on site as servers, and installing special monitoring software or plug-ins on remote clients' computers, users can see scenes thousands of miles away through the Internet, and realize single-channel and multi-channel video remote monitoring and recording.

2. Analog camera+network video server+computer network system

The signal output by analog camera is analog signal, the signal processed by computer is digital signal, and the digital signal transmitted in network is also digital signal. The network video server converts the analog signal of the analog camera into a digital signal, which is compressed and encoded by an efficient compression chip, and outputs the digital signal that can be transmitted in the computer network, thus realizing the transmission in the form of a digital signal in the computer network. Therefore, the network video server can also be called a video encoder. When one end of the video server is connected with the output signal of the analog camera, and the other end is plugged in with the computer network cable, then a gateway and a route are set on any computer in the Internet, an IE browser is opened, and an IP address or a domain name is input, so that a monitoring screen can be seen on the computer. If the analog camera is equipped with a tripod head, we can also control the camera to zoom, zoom and rotate through the computer. The network video server must be embedded with a real-time operating system, which can be either a Linux version or a Windows version. In terms of stability, the Linux version is better. Using the network video server, different cameras can be selected and equipped, which has greater flexibility.

3. Network camera+computer network system

Network camera is the integration of analog camera and network video server. A/D conversion and video server functions are built into the camera. Like the network video server, it can realize network communication and data transmission according to the network protocol, and can also receive and send alarm signals. This is more convenient, as long as the webcam is installed and plugged in, you can browse.

4.CDMA wireless network video monitoring system

The transmission mentioned above is wired transmission, but it is obviously difficult to use wired transmission in moving vehicles (cars), remote mines and mountainous areas. We can use mature wireless communication technology. The representative product here is China Unicom's Mobile Vision. Mobile video communication CDMA wireless network video monitoring system is a convenient product integrating CDMA data communication function and digital video coding function. It compresses the camera image through the video compression coding module and transmits it to the CDMA network through the intelligent wireless communication terminal, realizing the functions of video data interaction, sending/receiving, encryption and decryption, coding and decoding, link control and maintenance. The system can transmit real-time dynamic 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, and can monitor and manage remotely anytime and anywhere.

Explanation of common technical indexes of intransitive verbs

1, resolution

Image resolution simply refers to the number of points displayed horizontally and vertically on the screen. For example, 1024×728, where "1024" represents the number of points displayed horizontally on the screen and "768" represents the number of points displayed vertically. The higher the resolution, the clearer the image. The higher the resolution, the clearer the image display.

Step 2 be clear

Camera definition is expressed by lines, which are divided into horizontal lines and vertical lines. In practical engineering applications, we often take the horizontal line as the evaluation index of camera definition. The more lines, the higher the definition. The resolution of commonly used black-and-white cameras is generally 450-600, and that of color cameras is generally 330-480. The higher the value, the clearer the image. In general monitoring occasions, a 450-line camera can meet the requirements. For special occasions such as medical treatment and image processing, 600-line camera can get clearer images.

3. Automatic gain control (AGC)

In order to make the camera output standard video signals under different illumination conditions, automatic gain control is introduced into the video processing circuit, and gain feedback control is realized by detecting the average level value of video signals. A camera with AGC function will improve the sensitivity in low illumination, but at the same time it will amplify the interference signal and make the image look messy.

4. Backlight Compensation (BLC)

When the camera shoots in a backlight environment, a black image will appear on the screen. However, the backlight environment is inevitable in safety, and backlight compensation is needed at this time. When the backlight compensation function is introduced, if the camera detects that the video level of a certain area of the captured image is relatively low, the AGC circuit described above can improve and enhance the video level of this area, increase the amplitude of the output video signal, and make the whole image clear and bright. If the theme you want to see darkens because of the bright background, you can set BLC to on state to compensate for the strong backlight.

5. Electronic shutter (EE/AI) switching

At the back end of smart cameras, we can often see the EE/AI changeover switch. EE refers to the electronic shutter mode; AI refers to the automatic aperture lens mode. The electronic shutter of a camera is usually set to the automatic electronic shutter mode. Through the electronic shutter mode, the exposure time of CCD image sensor is adjusted according to the intensity of incident light, so as to obtain a clear image. The electronic shutter time is between1/50-1100000 seconds.

6, signal-to-noise ratio

Refers to the ratio of signal level to clutter level, including power supply clutter, random clutter, single frequency clutter, etc. Usually expressed in decibels (dB). The higher the signal-to-noise ratio, the less clutter and the higher the image signal quality. Signal-to-noise ratio should not be less than 48dB.

7. White balance

In order to restore the color of the object, the color camera must keep the white balance normal.

How to treat the parameters of surveillance camera?

IRLED stands for infrared ray. IRLED:25*6PCS+8*6PCS refers to the number of infrared lights, that is, the lens configuration is six or eight lights.

PCS stands for "chip", and 25*6PCS stands for six infrared LED lamps with a diameter of 25mm.

IRLEDWorkingDistance: the farthest working distance, such as infrared ray.

Because infrared lamps generally emit radiation and cannot converge far enough, they can't play the role of infrared irradiation. Generally, the working distance of low-power infrared lamp is about 50 meters, and the power is 100.

Working distance of irled: 100 m, that is to say, the normal infrared ray of the camera can reach the distance of 100 m, and it can be seen that there is no visible light within 100 m through the camera.

Lens: refers to the length of the lens. For a long-distance camera, the lens is relatively large.

Image sensor LmageSensorSHARP/ Sony: This is the chip of the surveillance camera.