Before understanding the analog monitoring system and digital monitoring system; First, we clarify two concepts, the concept and relationship of analog signal and digital information.

Analog signal: it is mainly a continuous signal relative to discrete digital signal. Analog signals are distributed in every corner of nature, such as the change of temperature every day, while digital signals are artificially Abstract signals with discontinuous amplitude values. Analog signal refers to the information represented by continuously changing physical quantities. The amplitude, frequency, or phase of the signal changes continuously with time, such as the currently broadcast sound signal, image signal, etc.

Digital signal: the value of amplitude is discrete, and the amplitude representation is limited to a limited number of values. Binary code is a kind of digital signal. Binary code is less affected by noise and easy to be processed by digital circuit, so it has been widely used. Because digital signals are represented by two physical states, their ability to resist material interference and environmental interference is much stronger than analog signals; In the signal processing of modern technology, digital signal plays a more and more important role, and almost complex signal processing is inseparable from digital signal; In other words, as long as the method of solving the problem can be expressed by mathematical formula, the digital signal representing physical quantity can be processed by computer.

In recent years, in the field of traditional TV monitoring, digital monitoring system has risen rapidly, and has occupied an increasing market share with its unique technical advantages. The video signal we usually say often refers to the analog video signal, and its recording mode is generally analog tape recording. Considering the signal attenuation of the video tape itself, with the increase of playback or replication times, its image quality will be irreparably degraded. Compared with the analog signal, the digital video signal comes from the digitized analog video signal. While maintaining the original image quality, it can be copied and played back at any time without loss. Due to its digitization characteristics, the digital video signal can be easily transmitted through different media such as magnetic disk, optical disk, data tape and even network Fast long-distance transmission.

< function >
Analog monitoring system:
1. The analog video signal from the analog camera is recorded, and its storage medium is generally analog tape (video tape)

2. Monitor the scene in real time through the TV monitor

3. The real-time monitoring and video recording of multiple monitoring sites are realized through the multi picture (picture) splitter, and each video picture is reduced to 1 / 4 / 9 / 16 of the original size

4. Use the panel buttons or the remote control to perform routine operations on the video recorder

5. Use the control keyboard (joystick) to realize the real-time control of the PTZ and lens on the monitoring site

6. The sequential retrieval and playback of the video on the monitoring site can be realized through the rewinding of the video tape, but the playback and video can not be carried out at the same time

7. In view of the limited recording time of video tapes, special personnel must be arranged to replace and eliminate video tapes regularly, and special rooms must be arranged for storing a large number of video tapes

8. In order to realize the function of motion detection and linkage alarm, detection and alarm devices must be installed on the monitoring site

9. It is difficult to complete post-processing (such as image cutting, scaling, etc.) and printing and backup of video signals

Digital monitoring system:
1. The analog video signal from the analog camera is digitized, compressed and recorded, and its storage medium is generally data disk

2. Monitor and monitor the site conditions in real time (25 frames / s) through computer display or TV monitor

3. Through the parallel processing technology of multi-channel (16 channels) video, the real-time (25 frames / s) monitoring and video recording of multiple monitoring sites can be realized. Each channel of video monitoring picture can be arbitrarily scaled to the full screen, and the video picture remains the original size

4. Use the mouse (the all-in-one machine adopts panel buttons and remote controller) for routine operation

5. The human-computer interaction interface is used to realize the real-time control of the PTZ and lens on the monitoring site

6. Take date, time, video channel and alarm events as indexes to realize fast and random retrieval and arbitrary proportion playback of on-site video

7. Because the system can automatically cycle video recording, regular automatic backup, and the hard disk has a long service life, there is no need to arrange special personnel to replace and eliminate video tapes, and there is no need to arrange a special room for storing video tapes

8. Video motion detection technology can realize the function of "recording when moving, recording when not moving" and linkage alarm function, without installing detection and alarm devices on the monitoring site

9. It is easy for post-processing (such as image cutting, scaling, etc.) and printing and backup of digitized video signals

10. The video recording and playback of the system can be carried out at the same time without mutual interference

11. It can realize multi-functional remote video monitoring and video recording through network transmission media such as telephone line, ISDN, LAN and broadband network. It can be seen that the digital monitoring system can not only complete all functions of the analog monitoring system, but also complete many functions that the analog system does not have. On the other hand, because the front-end equipment of the two monitoring systems are the same, on the premise of retaining the original wiring, PTZ, lens, decoder and other peripheral equipment, the smooth transition from analog system to digital system can be realized only by replacing the video recorder.

< performance >
Analog monitoring system:
1. Video recording quality: VHS
2. Video playback quality: continuously degraded with the increase of video tape use time and times
3. Storage medium: analog magnetic tape (video tape), easy to be disturbed by noise, easy to wear and difficult to store for a long time
4. Operation mode: panel button, remote control, control keyboard (joystick), retrieval and playback is very cumbersome
5. Operation interface: not yet
6. Maintenance method: manually replace, eliminate the video tape, archive and clean the magnetic head regularly
7. Equipment architecture: time delay (long time delay) video recorder, it is difficult to establish a large, complex and multi-functional monitoring system
8. Upgrade method: replace the system
Digital monitoring system:
1. Video recording quality: CIF or higher
2. Video playback quality: completely consistent with video recording quality without any attenuation
3. Storage media: hard disk, optical disc, data tape, etc., with strong anti-interference ability, not easy to be damaged and easy to be stored for a long time
4. Operation mode: mouse (all-in-one machine adopts panel button and remote control), which is simple and fast for retrieval and playback
5. Operation interface: graphical user interface (GUI), friendly, easy to operate, with online help or tips
6. Maintenance mode: maintenance free, automatic cyclic video recording, regular automatic backup, no manual intervention, and the service life of the hard disk is much longer than that of the video tape
7. Equipment architecture: industrial computer, PC and all-in-one computer, which is easy to use network technology to establish a large, complex and multi-functional monitoring system
8. Upgrade method: software upgrade
9. Video compression algorithms: M-JPEG, MPEG-1, MPEG-4, h264, etc
10. Operating system: Windows98 / NT / 2000 / XP / Vista, Linux, etc

< safety, stability and maturity >
Analog monitoring system:
1. The security is low, and the replacement of video tapes is convenient and fast, which may give criminals an opportunity
2. Stable and reliable operation, not easy to crash
3. The system is quite mature and difficult to improve technically

Digital monitoring system:
1. High security, any operation on storage, playback, parameter setting, etc. shall be subject to strict password verification
2. Industrial computer, all-in-one computer, WindowsNT / 2000, Linux: the work is relatively stable and reliable
3. PC and windows systems: the system tends to be mature and the technology continues to improve. Below, we summarize the previous text in the form of list: from the above comparison, it can be seen that the digital monitoring system has incomparable advantages in multi-channel video monitoring, random retrieval and playback, simultaneous recording and playback, network remote monitoring, monitoring video preservation, etc, With the continuous development of digital technology and the gradual expansion of application fields, the digital monitoring system will further mature, reaching and surpassing the analog monitoring system in terms of system stability and applicability.