Detailed explanation of basic terms of security technology
Vertical synchronization, color video composite signal synchronization, external synchronization, DC line lock and complete synchronization are different synchronization methods between cameras.
Fully synchronized
Global locking is the best way to fully synchronize two precision cameras such as broadcast studio cameras. It will synchronize: horizontal, vertical, even / odd area, color trigger frequency and phase.
Vertical synchronization is the easiest way to synchronize two cameras. The vertical drive frequency is used to ensure that the video can use the old switching period or four-segment machine to display several image sources on the same monitor. The vertical drive signal usually consists of pulses with a repetition frequency of 20 / 16.7 ms (50/60 Hz) and pulse widths of 1 to 3 ms.
Color video composite signal synchronization Color video composite signal represents video and color trigger signal, which means the camera can synchronize with external composite color video signal. However, although it is called color video composite signal synchronization, in fact only horizontal synchronization and vertical synchronization are performed, and there is no color triggered synchronization.
External synchronization
Very similar to color video composite signal synchronization. One camera can synchronize the video signal of another camera, and an external synchronization camera can use the input color video composite signal to extract horizontal and vertical synchronization signals for synchronization.
DC line lock
It is an ancient technology that uses DC 50/60 Hz power line current to synchronize the camera. Because the DC 24V power supply is widely used in most building fire alarm systems, it is very easy to obtain. Since the old models of switchers and split systems do not have a digital memory function, to maintain a stable image, synchronization between cameras is very necessary. DC line lock means that the cameras are synchronized to AC 50/60 Hz, and the time correlation and level between color channels / The vertical signal is not constrained and will result in poor color conversion (color phase design), so all users who use the AC line lock will inevitably lose good color conversion. Fortunately, current splitters and 16-channel composite processors and hard disk video recorders have internal memory to overcome this problem. Synchronization signals are no longer needed, so the AC line lock may be eliminated in a few years.
Colorless scroll
When a digital signal processor video camera is used under fluorescent lights, it can only produce images with severe color scrolling. The image will change from white to blue, pink and back to white, and so on. This is due to problems caused by AC power running at 50/60 Hz. The incandescent light bulb can provide stable light, and the light of the fluorescent lamp fluctuates due to the intensity and color of the alternating current changing at a speed of 8.3ms. The traditional camera calculates that the white balance needs 100 ~ 150ms (0.1 ~ 0.15), which is 8.5ms slower than AC, so it can never catch up. Only 8 cycles of the current image can clearly produce color scrolling.
BLC
It can provide ideal exposure of the target in front of a very strong background light, regardless of whether the main target is moved to the middle, up, down, left, or any position on the screen. An ordinary camera without super dynamic features only has a choice of shutter speed of 1/60 second and aperture of F2.0. However, a very bright background behind a main target or a point light source is inevitable and the camera will achieve The average value of all recent light and determines the level of exposure. This is not a good method, because when the shutter speed increases, the aperture will be closed and the main target becomes too dark to be seen. To overcome this problem, a method called backlight compensation is widely used on most cameras through weighted area theory. The image is first divided into 7 blocks or 6 areas (two areas are repeated), each area can be independently weighted to calculate the exposure level, for example, the middle part can be added to 9 times the remaining blocks, so one is in the middle of the screen The position of the target can be seen very clearly, because the exposure is mainly calculated with reference to the light level in the middle area. However, there is a very big flaw. If the main target moves from the middle to the top, bottom, left, and right of the screen, the target will become very dark, because now it is not distinguished and is not weighted.
F indicates the aperture of the lens, F stops 2: 1 and f3.4 mm indicates that the focal length of the lens is 3.4 mm.
Lenses F2.0 and f3.4 ~ 4 use a very economical form, which should be cheaper and widely used in single-board cameras. The aperture of the lens of F2.0 can collect half of the light of the human eye. The lens of f3.4 mm There is a 60-degree angle of view on a 1 / 4-inch CCD and a 90-degree angle of view on a 1 / 3-inch CCD, which is very close to the angle of view of the human eye. The two eyes of the human eye can contain a larger angle of view, generally 150 to 180 angles from person to person, but please remember that F stop and f focal length are only the basic parameters of a lens and do not represent quality.
Ultra-wide dynamic is a feature that allows the camera to see the image under very strong contrast. Wide dynamic cameras are dozens of times larger than traditional cameras with only 3: 1 dynamic range. Natural light is arranged from 120,000 Lux to 0.00035 Lux in a starry night. When the camera looks out the window from the inside, the indoor illuminance is 100 Lux, and the illuminance of the outside scenery may be 10,000 Lux, the contrast is 10,000 / 100 = 100: 1. This contrast can be easily seen by the human eye, because the human eye can handle a contrast ratio of 1000: 1, but the traditional closed-circuit surveillance camera has a lot of problems to deal with. The traditional camera only has a 3: 1 contrast performance, it can only Choose to use the electronic shutter of 1/60 second to get the correct exposure of the indoor target, but the outdoor image will be cleared (all white); or another way the camera chooses 1/6000 seconds to get the perfect exposure of the outdoor image, but the indoor The image will be cleared (full black).
Peak sensing mode
The exposure index is determined by replacing the average value of the entire image with the highlights of the image. Users who use the rule system can cope with the most demanding requirements, such as grabbing an image of a white point in the night, and also see this small bright white Details and colors.
CMOS
Full name is Complementary Metal-Oxide Semiconductor, Chinese translation is complementary metal oxide semiconductor. The manufacturing technology of CMOS is no different from that of general computer chips. It is mainly a semiconductor made of silicon and germanium, which coexist with N (charged-charged) and P (charged + charged) grades on CMOS. In semiconductors, the current generated by these two complementary effects can be recorded and interpreted as an image by the processing chip.
CCD
Full name is Charge Coupled Device, Chinese translates as charge coupling device. It is made of a high-sensitivity semiconductor material that converts light into electric charge, and then converts the electrical signal into a digital signal through an analog-to-digital converter chip. The digital signal is compressed and transmitted to the computer through the USB interface to form a computer. The collected image.
The concept of depth of field: when an object is in focus, all scenes from a certain distance in front of the object to a certain distance behind it should also be clear. The distance from front to back where the focus is quite clear is called the depth of field. The depth of field is divided into the foreground depth and the back depth of field. The back depth of field is greater than the foreground depth. The deeper the depth of field, the scene farther away from the focus can also be clear, while the shallow depth of field, the scene farther away from the focus is blurred.
focal length
It is an uncompromising optical parameter that any optical instrument has. From the optical principle, the focal length is the distance from the focal point to the center of the lens. For the lens, the focal length is very important. The focal length is proportional to the imaging size. The longer the focal length, the larger the imaging, and the shorter the focal length, the smaller the imaging. The focal length of the lens is inversely proportional to the viewing angle. The longer the focal length, the smaller the viewing angle, and the shorter the focal length, the larger the viewing angle. The focal length is inversely proportional to the depth of field. The longer the focal length, the smaller the depth of field, and the shorter the focal length, the greater the depth of field. The focal length is inversely proportional to the strength of perspective. The longer the focal length, the weaker the perspective, and the shorter the focal length, the stronger the perspective. The focal length is inversely proportional to the contrast. The longer the focal length, the smaller the contrast, and the shorter the focal length, the greater the contrast. The farther the focusing distance, the deeper the depth of field, and the closer the focusing distance, the shallower the depth of field. Therefore, when shooting a distant scene, you should choose a lens with a large focusing distance, and when shooting a close shot, you should use a product with a small focusing distance. The lens focusing distance is expressed in cm (centimeters), which can be described at a glance.
Switcher
There are two working modes: manual switching and automatic switching. The manual mode is to switch the switch to the desired way; the automatic mode is to delay the preset video in sequence. The switching time can be adjusted by a knob, generally in Between 1 second and 35 seconds. If monitoring is not required at all times, you can add a switch in the monitoring room, connect the camera output signal to the input of the switch, the output of the switch is connected to the monitor, and the input of the switch is divided into 2, 4, 6, 8, 12, 16 channels, the output is divided into single channel and dual channel, and can also switch audio synchronously (depending on the model).
Video server
It is a special computer equipment for compressing, storing and processing video and audio data. It is widely used in video surveillance, network teaching, IP video conference, advertisement insertion and video program on demand. The video server uses M-JPEG, H.261, H.263, MPEG-2, MPEG-4 and other compression formats, and compresses and encodes the video data to meet the storage and transmission requirements when it meets the technical specifications. With multi-channel input and output, multiple video and audio format interface. Can be equipped with SCSI, FC and other network interfaces for networking to achieve the transmission and sharing of video and audio data. It is composed of video and audio compression encoder, mass storage device, input / output channels, network interface, video and audio interface, RS422 serial interface, protocol interface, software interface, video and audio crosspoint matrix, etc. At the same time, it provides external phase lock And video processing functions.
Web camera
It is a new generation of camera produced by combining traditional camera and network technology. It can transmit the image to the other end with a network connection port through the network, and the remote viewer does not need to use any professional software, as long as the standard network browsing The camera (such as "Microsoft IE or Netscape" can monitor its image. The network camera has an embedded chip with an embedded real-time operating system. The video signal sent from the camera is compressed by the high-efficiency compression chip after digitization, and transmitted to the Web through the network bus Server: Users on the network can directly view the camera image on the Web server with a browser, and authorized users can also control the camera's pan / tilt lens movement or operate the system configuration.
Motion detection
The entire monitoring screen is divided into multiple small areas. The user can arbitrarily select the area in the area, and can set the sensitivity of the selected monitoring area to 1-20 levels. In this way, when something moves, it will be detected by the camera server and record at the same time.
Communication Interface
The communication interface in the security monitoring system is mainly for the input and output of video and audio. Therefore, the communication interface generally has the following types: RS-232, RS-485, general-purpose network interface, which can support various networking environments of PSTN, ISDN, and LAN, and has a USB2.0 ultra-high-speed data interface. , Optional with progressive scan VGA output interface, etc.
Monitor
It is the standard output of the monitoring system. Only with the monitor can we view the images sent by the front end. The monitor is divided into color and black and white, the size is 9, 10, 12, 14, 15, 17, 21 inches, etc., the commonly used is 14 inches. The monitor also has a resolution, which is expressed by the number of lines as the camera. In actual use, the number of lines of the monitor is generally required to match the camera. In addition, some monitors also have audio input, S-video input, RGB component input, etc. In addition to the audio input monitoring system, the rest of the functions are mostly used for image processing, and will not be described here.
Video amplifier
When the video transmission distance is relatively long, it is better to use a video cable with a thicker wire diameter. At the same time, a video amplifier can be added to the line to enhance the signal strength to achieve the purpose of long-distance transmission. Video amplifiers can enhance the video's brightness, chrominance, and synchronization signals, but interference signals within the line will also be amplified. In addition, there should not be too many video amplifiers in series in the loop, otherwise saturation will occur, resulting in image distortion.
The gimbal is an installation platform composed of two alternating currents, which can move horizontally and vertically. According to the use environment, it is divided into indoor type and outdoor type. The main difference is that the outdoor type has good sealing performance, waterproof, dustproof, and heavy load. The installation method is divided into side installation and ceiling installation, that is, whether to install the gimbal on the ceiling or on the wall. The shape is divided into ordinary type and spherical type. The spherical gimbal is placed in a hemispherical and spherical protective cover. In addition to preventing dust from interfering with the image, it is also concealed, beautiful and fast.
Embedded Systems
Refers to the operating system and functional software integrated in the computer hardware system. Simply put, the application software of the system is integrated with the hardware of the system, similar to the way the BIOS works. It has the characteristics of small software code, high automation and fast response speed. Especially suitable for systems that require real-time and multi-tasking.
Full-duplex: It can be sent and received at the same time. Full-duplex requirements: Separate channels for receiving and sending, which can be used to realize communication between two stations and star network, ring network, not for bus network.
Half-duplex: It is impossible to send and receive at the same time, and sending and receiving are time-divisional. Half-duplex requirements: the transceiver can share the same channel and can be used for various
Local area of ​​topology
The network is most commonly used for bus networks, and half-duplex data rates are theoretically half of full-duplex.
Directional curtain infrared detectors generally work in a two-way pulse counting mode, that is, from the A direction to the B direction, the B direction to the A direction does not alarm. With the ability to recognize the direction of intrusion, the user enters the warning zone from inside to outside without triggering the alarm. Returning within a certain period of time will not trigger the alarm. Only the illegal intruder intruding from the outside will trigger the alarm, which greatly facilitates the user's defense. Activities in the security zone without triggering the alarm system.
Automatic high-speed tracking dome
It integrates optics, electronics, machinery, information processing and network. It is composed of camera, power transmission, motion control device, image analysis, recognition, compression and communication based on high-speed parallel processing. With video camera, position control, azimuth and lens preset, moving target detection, identification and tracking, flame and smoke detection alarm and other functions. When the moving target enters the field of view of the spherical camera, the high-speed DSP chip is used to calculate the difference between the previous image and the current image. When a certain value is reached, a certain part of the frame is determined to be a moving object, and then The dome camera automatically issues instructions to the dome camera head, and so on, so as to control the spherical camera to achieve continuous tracking of moving objects without the need for human operation or computer system support.
Line lock synchronization
(LINE LOCK) is a synchronization method that uses AC power to lock the field sync pulse of the camera. When there is network wave interference caused by AC power in the image, set this switch to the line lock synchronization (LL) position to eliminate AC power interference.
Automatic gain control
The video signal output by the camera must reach the standard level specified by the TV transmission, that is, in order to be able to output a standard video signal under different scene illumination conditions, the gain of the amplifier must be adjusted in a large range. This gain adjustment is usually done automatically by detecting the average level of the video signal. The circuit that implements this function is called an automatic gain control circuit, or AGC circuit for short. The sensitivity of the camera with AGC function will be improved at low illumination, but the noise at this time will also be more obvious. This is because the signal and noise are amplified simultaneously.
Sound source
It is the source of the sound. If there is no sound source, there is no way to restore the sound with the sound system. The sound source has two meanings. First, it refers to the carrier that records the sound. Only when the sound is recorded on a certain carrier, can it be said that the sound on the carrier is restored by the audio equipment. These carriers are the source of the sound in the audio system. So it's called sound source. Another meaning of sound source refers to the device that plays the sound source carrier. Signals that are continuous in time and whose amplitude changes continuously with time are called analog signals (for example, sound waves are analog signals, and the current and voltage signals transmitted in the audio system are also analog signals), and the audio source that records and processes analog signals is an analog sound source, such as magnetic tape / Deck, LP / LP record player.
Analog source
The recorded and processed signal is the original face of sound (accurately speaking, it should be an electrical signal converted from sound), which can be directly amplified by a traditional amplifier, which is convenient and direct to process; digital sound source recording and processing are 0 and 1 The abstract binary data stream formed by arrangement and combination is very unintuitive. Sound waves are analog and cannot be used directly for digital audio sources. They must be converted to digital signals through conversion equipment before they can be recorded on a digital audio source carrier. During playback, the data read by the digital audio source device cannot be directly amplified by a traditional amplifier, and must be converted to an analog signal first. It can be seen that the digital audio signal processing process is much more complicated. However, the advantages of digital audio sources are outstanding: the signal-to-noise ratio and dynamic range are far superior to analog audio sources. The quality of the signal does not deteriorate after multiple replications and multiple transmission links. This analog audio source cannot be done anyway.
AVS
It is an audio and video coding technology standard independently developed by China. The AVS Working Group was established in June 2002, and the first working meeting began in August of that year. After 7 AVS official working meetings and 3 additional video group meetings, after a year and a half, 182 proposals were reviewed, and 41 proposals were adopted successively. The video part of AVS was finally finalized on December 19, 2003. The characteristic core technologies in AVS-video include: 8x8 integer transform, quantization, intra prediction, 1/4 precision pixel interpolation, special inter prediction motion compensation, two-dimensional entropy coding, deblocking in-loop filtering, etc. The current AVS-video technology can realize the compression of videos in different formats such as standard definition (CCIR 601 or equivalent) and low definition (CIF, SIF).
Real-time editing technology
It means that the hard disk video recorder can process the collected raw data in real time and convert it into a standard MPEG-1 or MPEG-2 format image file, which is directly stored on the hard disk without data backlog and loss in the middle; this is mainly related to the computer Compared with burning, when the computer burns, the original data is collected first, and then the data is processed and converted into a standard MPEG-1 or MPEG-2 format image file. Real-time codec technology requires that the speed of the entire system is fast enough, otherwise, it can only be achieved by reducing the image quality and data volume.
Super HAD image sensor
Built-in CCD image sensor using "Super Hole AccumulaTIon Diode (HAD)" electronic image quality improvement technology to improve CCD sensing performance and strengthen digital signal processing functions, effectively reduce noise and reduce unnecessary interference when shooting images, so that The picture is clearer and brighter, the color gradation is more distinct, and it is particularly effective when there is insufficient light source on the scene or when shooting night scenes.
White balance
That is White Balance. The color of the object will change due to the color of the projected light, and the images taken in different light situations will have different color temperatures. For example, a photo taken in an environment illuminated by a tungsten filament lamp (electric bulb) may be yellowish. Generally speaking, there is no way for a CCD to automatically correct light changes like the human eye. Therefore, through the correction of white balance, it will immediately adjust the intensity of the red, green and blue colors of the entire image according to the characteristics of the image in the current portrait to correct the errors caused by external light. In addition to the automatic white balance or specific color temperature white balance function, some cameras also provide manual white balance adjustment.
Variable stream codec technology
The codec can automatically adjust the bandwidth according to the amount of data. When the image changes faster and the color is richer, the allocated bandwidth is larger; when the image changes slowly, the color is less rich, the allocated bandwidth is smaller. While ensuring the quality of image recording, the hard disk space is saved to the maximum.
Fixed stream codec
The provided bandwidth is fixed. Regardless of the amount of data, when the image is rich in color and changes rapidly, the bandwidth is often not enough to reduce the quality of the video. It seems that the image is a bit paused or the color changes. When the amount of image data is not large, Has more bandwidth, wasting storage space.
Pixel
It is one of the important indicators to measure the camera. Some products will be marked with 300,000 pixels or 350,000 pixels in the box. In general, products with higher pixels have better image quality. But on the other hand, it is not that the higher the pixel, the better. For the same screen, the higher the pixel, the stronger the ability to parse the image. In order to obtain a high-resolution image or screen, the amount of data it records must be large. The requirements for storage devices are much higher, so you should pay attention to the related storage devices when selecting.
Access control system
It is a brand-new access management method: allow those with authority to enter the designated area, and reject those without authority. The protagonist of the system is the card reader or password keyboard installed on the door side. They transfer the read data to the local controller, and confirm whether they can pass according to the database compiled in advance.
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