A brief discussion on security: Talking about the selection and technological advancement of network cameras

Network cameras integrate video compression and network transmission processing modules based on analog cameras. Therefore, they have the technical characteristics of both analog cameras and video servers, but they are not a simple combination of the two. The unique structural design and implementation method determine that they have their own technical characteristics.

Technical features of network cameras

From the perspective of hardware structure, network cameras integrate video compression and network transmission processing modules on the basis of analog cameras. Therefore, they have the technical characteristics of both analog cameras and video servers, but they are not a simple combination of the two. The unique structural design and implementation method determine that it has its own technical characteristics.

1. Video Compression

Video compression is the most basic technical requirement for network cameras. At present, the video processing chip of network cameras is mainly ASIC, and video compression adopts standards such as MPEG-2, M-JPEG, MPEG-4 and H.264, among which H.264 is the mainstream. Recently, network cameras based on TI Davinci chip have been launched. Davinci is a SoC system with the characteristics of ASIC efficient processing, while taking into account the innovative flexibility of CPU and DSP. It has a DSP main processing system and an ARM9 subsystem. Another important feature is that it has extremely rich interfaces, which are very useful for the functional development of network cameras. Some of the following features are based on this feature.

2. Highly integrated

The network camera has more than just the image acquisition function of the traditional analog camera. It is already a front-end processing system with quite a rich heterogeneous bus access function, such as VOIP, alarm, 232/485 serial device access, etc. In addition, it can also send alarm signals such as motion detection, video loss, lens cover, storage abnormality, etc. to the back end through the network. The network camera can have an embedded storage system, usually using an SD card. The current capacity of SD cards ranges from 8MB to 4GB. The SD card can be used as a temporary storage device for images when the network fails. When the network is restored to normal, the video can be uploaded, which can effectively ensure the continuity and integrity of the video data. Another use of the SD card is to store important alarm images locally and upload them to the back end at the same time, so that the video data will not be lost due to unreliable network transmission.

3. Power over Ethernet (POE)

POE is a network power supply technology that has developed rapidly and been widely used in recent years. POE (Power Over Ethernet) refers to a technology that can provide direct current to some IP-based terminals (such as IP phones, network cameras, etc.) while transmitting data signals without changing the existing Ethernet Cat.5 wiring infrastructure. In this way, network cameras no longer need to be powered by other power sources. The centralized use of UPS (uninterruptible power supply) can ensure uninterrupted operation of the equipment for a period of time (depending on the UPS), and also simplify management. The IEEE802.3af standard is a new standard based on the Ethernet power supply system POE. The standard requires that the power consumption of devices powered by POE cannot exceed 12.95W.

Now, most network switches provided by manufacturers support PoE function. If you have already installed the corresponding ordinary switch equipment, you can realize the PoE function by simply adding a midspan to the switch. Among them, the main function of the midspan is to load power to the network cable. [page]

4. Wireless access

Although most buildings now have wired networks installed, and network cameras can be connected to the network through wired means, wireless access network solutions are more attractive in reducing engineering complexity and costs. For example, in some places where the camera position needs to be changed from time to time but no rewiring is desired (such as supermarkets), or where wiring may affect the aesthetics of the entire internal building, wireless access network solutions can easily solve these problems.

The common wireless access method for network cameras is wireless local area network (WLAN) access. Wireless local area network refers to a wireless network with a small span, usually located indoors, and the effective distance is generally not more than 100 meters (802.11g). There are many standards for wireless local area networks. Wireless network cameras generally use IEEE802.11b or IEEE802.11g standards. 802.11g is an improved version of 802.11b, with a data transmission rate of up to 54Mbps.

5. Security

Network cameras can provide three forms of security features. The first is user security management, such as user registration, permission management, etc. The second is IP/MAC address binding, which only allows computers with bound IP/MAC addresses to access; the third is to use general network security technology based on security levels.

At present, some manufacturers have launched a series of network cameras based on Davinci, which use the H.264 encoding engine with independent intellectual property rights, have functions such as PTZ, alarm input/output, voice intercom, SD storage, etc., have network functions such as heartbeat, SADP, WebServer, and support IEEE802.11g wireless access.

How to Choose an IP Camera

Image quality

Image quality is the soul of the camera and one of the important indicators that need to be paid attention to. Good image quality comes from the lens and the imaging device. The image quality of the camera lens will affect the signal quality output by the imaging device. We can compare the lens to the human eye, and the imaging device to the retina.

1. Lens

There are many types of lenses, but even the same type of lens has a very different image quality, which is mainly due to factors such as material, processing accuracy and lens structure. It also leads to huge differences in the price of lenses of different grades, ranging from tens of yuan to tens of thousands of yuan. The more famous ones are the four-element three-group Tessar lens and the six-element four-group double Gauss lens. A good lens will have good performance in terms of resolution, sharpness, aperture coefficient, etc., and will also have better correction for various aberrations, but at the same time its price will be several times or even hundreds of times higher.

Aberration is an important aspect that affects image quality. There are six common aberrations: spherical aberration, coma, chromatic aberration, astigmatism, field curvature, and distortion. Therefore, the commonly used lenses are composed of multiple lenses and multiple groups of lenses plus multi-layer coatings. The purpose is to solve the aberration problem and make the image clearer, sharper, and more realistic in color.

2. CCD or CMOS

The main difference between CCD and CMOS in manufacturing is that CCD is integrated on semiconductor single crystal materials, while CMOS is integrated on semiconductor materials called metal oxides. There is no essential difference in the working principles.

From the manufacturing process, CCD manufacturing process is more complicated, and only a few manufacturers, such as Sony, Panasonic, Sharp, etc., have mastered this technology, so the price of CCD cameras is relatively expensive. In fact, after technical transformation, the actual effect gap between CCD and advanced CMOS is very small. Moreover, the manufacturing cost and power consumption of CMOS are lower than CCD, so many low-end camera manufacturers use ordinary CMOS photosensitive elements as core components.

In terms of imaging, CCD has good image transparency and sharpness under the same pixel, and can guarantee basically accurate color reproduction and exposure. However, ordinary CMOS products often have average transparency, weak color reproduction ability of real objects, and poor exposure. Due to its own physical characteristics, there is still a certain gap between the image quality of ordinary CMOS and CCD. However, due to its low price and high integration, it has been widely used in the camera field.

At present, many low-end entry-level cameras use cheap low-end CMOS chips, and the image quality is relatively poor. Popular, advanced and professional cameras use CCDs of different grades, and some professional or semi-professional digital cameras use advanced CMOS chips. The X3 chip, which represents the future development of imaging technology, is actually a CMOS chip. In summary, it is not possible to generalize which is better between CCD and CMOS, but for now, the image quality of cameras with CCD chips commonly used in the field of surveillance cameras is better.