For video surveillance, image definition is undoubtedly the most critical feature. The clearer the image, the more obvious the details, the better the viewing experience, and the higher the accuracy of application services such as intelligent analysis. Therefore, image definition is the eternal pursuit of video surveillance. The standard for measuring image sharpness is resolution, which is measured in pixels. The higher the value, the clearer the image. The difference between HD and SD is reflected here. The dividing line between the two is megapixels or 720p, and HD is when it reaches megapixels or 720p. (1) 1080i format is a standard digital TV display mode. 1125 vertical scan lines, 1080 visible vertical scan lines, 16:9, resolution 1920 × 1080, interlaced / 60Hz, line frequency 33.75khz. (2) 720p format is a standard digital TV display mode. 750 vertical scan lines, 720 visible vertical scan lines, 16:9, resolution 1280 × 720, line by line / 60Hz, line frequency 45khz. (3) 1080p format is the standard digital TV display mode. 1125 vertical scan lines, 1080 visible vertical scan lines, 16:9, resolution 1920 × 1080 progressive scan, professional format.

 

2、 Advantages of HD monitoring

 

HD has more advantages than SD in terms of resolution, display effect and fluency. In terms of resolution, the resolution of 720p is 9 times that of CIF, and the resolution of 1080i / 1080p is 20 times that of CIF. Under the same display environment, HD will be much clearer. From the display effect, HD supports both large screen display and 16:9 wide screen display, which can greatly enhance the user‘s viewing experience. In terms of fluency, HD supports higher frame rates. For example, both 720p and 1080i / 1080p can support 60 frames / s or 60 fields / s, and its image fluency is twice that of SD. Therefore, HD monitoring is one of the most mainstream trends in the development of the monitoring industry. For customers, HD is meaningful only when it includes front-end, platform, storage, browsing, display and other links. Therefore, in order to realize real HD monitoring, HD must be fully supported from the aspects of video source acquisition, video signal coding and compression, video signal transmission, video browsing, video file playback and so on.

 

3、 Application of HD monitoring in security field

 

☆ front end

 

Before that, the security industry mostly used simulation systems. Compared with these traditional closed-circuit television monitoring systems, HD cameras do not need coaxial cables and huge video distributors; Less equipment is required for installation, which can greatly reduce the wire rod, so as to greatly reduce the project cost; At the same time, HD network camera uses broadband network to transmit images, which is very cheap. It can make full use of network resources, enhance the flexibility of monitoring range, and directly realize remote monitoring by using network update software.

 

☆ transmission

 

The transmission technology of monitoring system mainly includes video baseband transmission, optical fiber transmission, network transmission, microwave transmission, twisted pair balanced transmission and broadband common cable transmission. Each technology has its own characteristics and application level. In the past, because optical fiber transmission has the advantages of small attenuation, wide frequency band, no electromagnetic wave interference and good confidentiality, optical fiber dedicated line transmission was once the best way to solve the high-speed transmission of long-distance video surveillance. With the rapid development of network technology, various broadband networks are emerging one after another. In addition to the optical fiber private network built by enterprises reaching Gigabit bandwidth, LAN is also gradually developing towards 1000m and 10000m. At the same time, major operators are also vigorously developing EPON and GPON optical networks to make the bandwidth reach more than Gbit. These provide a better carrier for the efficient transmission of high-definition video images in the network, and make the network transmission become another best choice for long-distance audio and video transmission.

 

At present, the uncompressed HD video signal after acquisition has two transmission modes: analog and digital. The analog transmission generally adopts YPbPr component transmission. One HD video signal needs three coaxial cables to be transmitted at the same time. Digital transmission generally adopts DVI, HDMI or HD-SDI transmission. The transmission distance of DVI or HDMI is only a few meters, which is not suitable for monitoring transmission. Although HD-SDI can transmit about 100 meters, it has high requirements for coaxial cable and the price of cable is very expensive. If the HD video is compressed efficiently at the front end and then transmitted through IP network, the transmission cost is equivalent to the networked transmission cost of standard definition monitoring.

 

Due to the limitations of HD video transmission on WAN, strengthening bandwidth construction is an important way to solve the problems of HD transmission and network bandwidth. In addition, because HD occupies higher network bandwidth, the use of network bandwidth should be carefully designed when establishing HD system, especially large number HD system. For example, 100M Ethernet can only carry 5 ~ 6 channels of high-definition images at the same time (considering the collision listening characteristics of Ethernet). If multiple users access the same video source, the bandwidth will be larger. Therefore, the use of system design, multicast, forwarding and other technologies is particularly important.

 

☆ storage

 

At present, the storage methods commonly used in the security system include Das direct connection, NAS network hard disk and IPSAN. Among them, IPSAN adopts Ethernet transmission of IP architecture, which has good scalability, sharing and low shared application cost. It is one of the main technologies used in large and medium-sized centralized monitoring storage at present. These storage methods are very mature technologies in the IT industry, and most of the storage media are general data hard disks in it, with a capacity of more than TB (based on 1g data per channel per hour, 1TB data hard disk can store 720p video images for 1000 hours or 1000 cameras recording data for 1 hour at the same time), Now 2TB data hard disk has gradually come into people‘s attention. With the continuous expansion of the scale of specific HD monitoring projects, Pb mass storage solutions for large HD monitoring systems will be widely used.

 

For HD monitoring system, the security requirements of HD video storage are also very high, especially the playback of stored video. Whether the video can be played back depends on several aspects:

 

1、 Whether the storage device has sufficient mixed read-write performance to ensure that the storage device can meet the playback of multi-channel video while writing a large number of HD video. The mixed read-write performance is insufficient, which may not only affect the normal video writing and playback, but also cause the subsequent video to be completely unable to write.

 

2、 The security and stability of the storage system, advanced RAID technology and highly reliable enterprise disk can effectively reduce the possibility of data loss caused by disk damage and ensure the real-time availability of HD video.

 

3、 Data backup, images of important places or important images of ordinary places in a certain period of time often need backup to ensure that the video is available at any time for a period of time. Generally, it can be saved to multiple storage devices at the same time during video acquisition, or a single file can be saved first and then copied to another storage device. Multiple saving or backup of important video files is a problem that must be considered in the design of HD monitoring system.

 

4、 The effectiveness of the platform software media management system is mainly the database structure design of the background of the media management system. Whether the target video can be retrieved quickly, accurately and effectively through keywords is an important indicator of the media management system. Otherwise, even if the HD video is saved, it may not be retrieved and used for image call and image analysis, so the image storage becomes meaningless.

 

In addition, intelligent analysis and data mining functions also fully reflect their application value in the storage system. Taking the intelligent building project as an example, the storage time can be expanded from 3 months or half a year to one year. Coupled with the later expansion of front-end monitoring points, the storage capacity required is greater. If the intelligent analysis module is installed and combined with time and alarm trigger storage, the space required for video storage will be greatly reduced. In some important occasions (such as airports and customs) entrance, the HD or video cameras can be compared with the background database to determine whether they are suspect or illegal vehicle. If the information matches the blacklist information, it will alarm and link the supporting system.

 

☆ the management platform is facing the increasing scale and complexity of projects in the intelligent building industry