Compared with network cameras, analog cameras can only transmit unidirectional video signals, and their performance is limited by DVR and operator level. However, the network camera can transmit full-duplex digital information and can be effectively integrated with other devices in the system, thus achieving a higher performance level in a distributed and extensible environment. Network cameras can communicate with multiple application systems in parallel to realize various functions, such as detecting motion in a picture or sending video streams in different formats.
Analysis: Congenital deficiency of analog camera
Why can't analog cameras cross the threshold of high definition? The insurmountable gap in HD is enough for many analog camera manufacturers to sigh. The fundamental reason why analog cameras can't cross the threshold of high definition lies in their inherent shortcomings.
Interlaced scanning: traditional analog cameras use interlaced scanning, and analog video signals are transmitted to DVR at the back end through coaxial cable for compression coding. Before high-definition D 1 video compression, it is necessary to combine odd fields and even occasions into one frame. Although there are various advanced synthesis algorithms, it will still cause some problems, such as vertical edge sawtooth, line flicker effect, moving picture blur and so on. This is also one of the fundamental reasons why the video quality of hard disk video recorder is far less than that of preview video.
Resolution: The traditional analog camera is born out of the old analog TV mechanism, and the original resolution is limited by the standard of analog TV. The vertical resolution in PAL system is 625 lines, and after blanking, it is 575 lines, with a maximum of about 540 lines. The highest resolution of traditional analog cameras can reach about D 1 or 4CIF, about 400,000 pixels, while high-definition network cameras can easily reach millions or even tens of millions of pixels without this limitation.
Color reproduction degree: the composite analog video signal output by the analog camera contains brightness signal and color signal, which are in the same frequency range. However, when the composite video is transmitted to the video capture chip, the video capture chip should not only do A/D conversion, but also do brightness and color separation. Because it is difficult to completely separate brightness and color signals, we often find that traditional analog video surveillance is prone to color penetration and noise. Digital high-definition cameras, on the other hand, have no trouble in separating bright colors, and colors can be more realistic.
Analog transmission: traditional analog cameras need to transmit analog signals over a long distance, which is prone to weak electromagnetic dry signals. The scene environment is complex and changeable, and the analog signal itself is easily disturbed by external factors such as electromagnetism and thunderstorm. It is often seen that the image at the back end of transmission fluctuates up and down, and ripples, flicker and Xue Huadian appear. A/D conversion is needed after transmission to DVR, and a lot of picture details and quality are lost in the process of A/D conversion. Therefore, the D 1 resolution of analog video is only a theoretical value, and the definition in practical application is completely lower than the theoretical value. High-definition network camera adopts the whole process of pure digital signal processing and transmission. Firstly, it scans the optical signals collected by CMOS image sensor line by line and directly converts them into line-by-line digital signals, then transmits them to DSP or special ASIC chip for video image compression coding, and finally outputs digital compressed video through the network. Because the whole process is digitized, digital cameras have incomparable advantages over traditional analog cameras in anti-electromagnetic interference, progressive scanning and picture resolution.
Analysis: the difference between webcam and analog camera
According to the recording mode of image signals, cameras can be divided into analog cameras and digital cameras. Although digital cameras are widely used at present, analog cameras cannot be completely replaced by digital cameras because of their own characteristics. In order to help readers know more about the relevant information, we will explain the theme of analog cameras in this series of drafts.
Analog camera, the front end uses interlaced scanning CMOS/CCD photoreceptor to convert optical signals into analog electrical signals, and then outputs them to DSP, which carries out A/D conversion and color adjustment, and then carries out D/A conversion to modulate them into PAL/NTSC TV signals for output.
Webcam can be regarded as a combination of camera and computer. It can capture images and transmit them directly through IP network, so that authorized users can watch, store and manage video data in local or remote locations through standard IP-based network infrastructure.
1, image
Webcam: People can see more clearly, which has always been the goal that people pursue. The webcam can output 100w, 200w, or even 300w500wa800w pixel images.
Analog camera: Only d 1 can realize cif output.
Step 2 monitor
Webcam: Built-in network allows you to manage and view images using a standard web browser on your PC. Ability to remotely manage and view images. The network camera can store the image data on the remote hard disk, which is easy to find and store and will not be destroyed.
Analog camera: closed circuit, only internal monitoring, not remote monitoring. Video materials can only be stored locally, not viewed remotely, and are easily destroyed by criminals.
Step 3 synthesize
Webcam: Built-in operating system. Using a standard WEB browser on any PC, you can manage and view images, and use it with multi-screen management software * * * to realize multi-channel monitoring, and the number of channels is unlimited. Without increasing the hardware cost.
Analog camera: Analog camera should be connected to DVR (Digital Video Recorder). Literally, it does not mean that the recording medium is a tape or a hard disk. ), the number of DVR paths is limited, and after the DVR is full, the cost of hardware will also increase when the projector is added.
4. Device
Webcam: Just connect the webcam to the nearest network and assign an IP address. It can use the existing network as a transmission platform without wiring.
Analog camera: Connect the coaxial cable to each camera and connect it to the control platform, video recording equipment and display equipment. Every time a route is added, it needs to be rerouted, and there is no ready-made network available.
Remote control of camera and cost comparison
5. Distant
Network camera: it can be managed remotely, such as video recording setting, cloud mirror control, alarm setting, two-way intercom, upgrade management and other functions.
Analog camera: you can only watch images locally for management.
6. Expansibility
Webcam: You can easily add more webcams to your system.
Analog camera: It is very difficult to expand the work. Each analog camera needs a dedicated cable. Using a long cable will affect the image quality.
7. expenses
Webcam: The cost of using high-quality network cable is usually 30% to 40% lower than that of standard coaxial cable. A network cable can support hundreds of network cameras and other devices at the same time. IP-based network infrastructure is usually in an appropriate position, which means that the cost of building a system can be reduced to only include the cost of webcams.
Analog camera: Coaxial cable is very expensive. The standard coaxial cable of RG59750hms is 30% to 40% more expensive than the high-quality network cable. Each analog camera needs a cable. If there are many cameras, you must buy a lot of morning cables and spend money to install and deploy them. Manpower and maintenance costs are high, and the system construction costs will also include the costs of analog cameras, video recorders and videotapes.
The network camera has its own independent IP address, which can directly connect to the network, and has built-in intelligent functions such as Web server, FTP server, FTP client, email client, alarm management, programmable ability and so on. Network cameras do not need to be connected to a PC, they can run independently and can be placed anywhere with an IP network interface. On the other hand, ordinary webcams used in * * * can only work normally if they are connected to a PC through USB or IEEE 1394 port.
In addition to video information, network cameras can also realize many other functions through the same network connection, and transmit some other useful information, such as video motion detection, audio, digital input and output (which can be used to realize alarm linkage, such as triggering alarm or activating on-site lighting), serial port transmission of serial data or driving PTZ equipment. The image cache in the network camera can also save and send the video images before and after the alarm.
interphone
Document 666
Notice of the Ministry of Industry and Information Technology on matters related to frequency planning and use management of special interphones in 150MHz and 400MHz bands is as follows:
In order to meet the social demand for digital walkie-talkies, promote the healthy development of digital walkie-talkies, and further improve the spectrum utilization rate, the Ministry of Industry and Information Technology issued the Notice on Matters Related to Frequency Planning and Use Management of Special Walkie-talkies in February 2002 150MHz and 400MHz bands, which provided a formal basis for the development of digital walkie-talkies in China. The notice reads as follows:
1. The frequency range of 150MHz and 400MHz special interphone specified in this paper is: 137 MHz- 167 MHz, 403MHz-423.5MHz, among which, the management of special frequency stations for water services is still implemented according to the current documents. In areas where water services are not used, the special frequency band for water services can be used as the special walkie-talkie frequency, but the frequency band 144MHz- 146MHz is amateur service's special frequency band and is not used as the special walkie-talkie frequency. 409.75MHz-409.9875MHz public walkie-talkies are still implemented according to the current documents; In order to meet the demand of small-scale internal paging service, seven frequency points are planned for this service in the frequency band of 137MHz- 167MHz.
Secondly, the channel interval of 150MHz and 400MHz special interphones is adjusted from 25kHz to 12.5kHz, and one or two time slots can be arranged for each channel; Among them, the frequency interval between 150MHz band and 400MHz band is 5.7MHz and 10MHz respectively.
3. Considering the demand for walkie-talkie frequency in major events and emergencies, some frequencies are planned as national special frequencies in 150MHz and 400MHz respectively. The national special frequency shall be uniformly managed by the national competent radio department, and no individual or unit may use it without authorization. In case of temporary major activities and emergency needs, all localities should report to the competent national radio department for approval before use.
Four, 150MHz, 400MHz band special walkie-talkie frequency distribution and use planning and frequency station localization management. Local radio management agencies can plan, allocate and use the frequencies that can be allocated or assigned by provinces (autonomous regions and municipalities directly under the Central Government) on the basis of the frequency allocation scheme in Annex I, combined with local actual conditions. In the planning process, local radio management institutions should, in principle, ensure the continuity of business use for special purposes such as public safety, safe production, disaster reduction and relief; For some trans-regional requirements, it is necessary to fully coordinate the radio management agencies of neighboring provinces (autonomous regions and municipalities directly under the Central Government). Before the implementation of the local planning scheme, it shall be reported to the competent national radio department for the record. All localities should take measures to make the transition between the old and new planning, and complete the transition within 6 years from the date of implementation of this article.
Five, within six months from the date of implementation of this article, the walkie-talkie units that have gone through the examination and approval procedures for frequency stations throughout the country shall go through the examination and approval procedures for frequency and setting again with the local radio management institutions. After the implementation of this article, if a new station is applied for, the local radio management institution shall assign and manage the frequency according to this planning scheme; For the existing legally established units, after the expiration of the frequency use period, the frequency should be re-assigned according to this planning scheme. In order to avoid the loss caused by replacing the existing equipment during the transition period, the local radio management organization can provide the necessary information such as the purchase date of the existing equipment, the radio license, and the payment certificate of the frequency occupation fee, and apply for extending the service period of the frequency.
Six, the production, import, sale and use of radio transmitting equipment, must obtain the type approval certificate of radio transmitting equipment issued by the Ministry of industry and information technology. Since the implementation of this article, according to the Radio Frequency Technical Index of Digital Intercom Equipment in 150MHz and 400MHz Band (see Annex II), the radio transmitting equipment model of digital walkie-talkie equipment in this band has been approved. At the same time, from 2011110, the model approval of analog walkie-talkie equipment in this frequency band will be stopped, and the analog walkie-talkie equipment that has obtained the model approval certificate will not be extended after its expiration. The technical indicators for model approval of walkie-talkie equipment special for water business continue to use the original analog walkie-talkie equipment indicators, and the name of the model approval equipment is marked as "water business". The technical indicators of public walkie-talkie equipment model approval are still implemented according to the current documents. 150MHz frequency band paging equipment type approval technical standards shall be formulated separately.