Spherical network cameras aim at "technical focus"

　   Abstract: A few years ago, in the process of video surveillance networking, analog dome cameras were gradually transformed into standard-definition network dome cameras. However, due to the limited R&D capabilities of traditional analog dome camera manufacturers and some small-scale dome camera manufacturers in terms of network, there are not many manufacturers developing network dome cameras. In addition, the cost advantage is not obvious, so standard-definition network dome cameras are not widely promoted and used in the market.

　　With the continuous development of high-definition video surveillance, ball machines also require high-definition video, including 1.3 million and 2 million pixels, so various manufacturers are vigorously developing high-definition balls, including network high-definition balls and digital high-definition balls. Among them, digital high-definition balls transmit uncompressed digital video signals, and the data transmission interface is the SDI interface. Due to its limitations such as high networking and supporting equipment costs, it is not widely used at present. Network high-definition balls are the fastest growing and have a large market demand. Since users are very concerned about the image quality at night, the use of network high-definition balls with infrared is very large, far exceeding that of non-infrared high-definition balls. Now there are some public model infrared high-definition balls on the market. Except for the movement and network board, the other parts are produced by public model manufacturers, with relatively low costs and large sales. Of course, manufacturers with R&D capabilities develop all parts by themselves, and their product functions, performance, reliability, quality, cost, etc. can be controlled by themselves, and they can be differentiated.

　　At present, network high-speed balls are still in the development stage, and there is still a lot of room for development. Its development direction is high-definition, infrared, low illumination, and low bit rate. First of all, in terms of clarity, gun cameras and hemispheres already have 5 million or even 8 million pixels, but high-speed balls only have a maximum of 3 million pixels. There is a bottleneck here, which is the core lens of the ball machine. At present, the core lens cannot reach a very high pixel, and a breakthrough is needed; secondly, in terms of infrared fill light, this will be the direction that all manufacturers have been working hard on, which will be discussed later; again, in terms of low illumination, there is still room for exploration, such as improving lens transmittance, optimizing ISP and 3D noise reduction, etc., and you can also choose a better sensor. Generally speaking, the larger the sensor target surface, the better the low-light effect. Of course, the sensor target surface must be matched with a core lens, so it is necessary to vigorously develop a core lens with a large target surface to match the sensor with a large target surface and low light. Finally, in terms of low bit rate, since the high-definition bit rate is relatively large, the H.264 encoding standard is used, the bit rate of 720P/30fps is about 2Mbps, and the bit rate of 1080P/30fps is about 4Mbps. The required transmission bandwidth and storage capacity are relatively large. If you can find a way to reduce the bit rate, it will save transmission and storage costs. The HEVC/H.265 standard released by the ITU-T organization can reduce the bit rate by about half compared to the H.264 standard, which is the direction of subsequent high-definition ball encoding development.

　　Discussion on infrared high-definition ball technology

　　The main components of the infrared high-definition ball include the interface part, power part, encoding part, pan-tilt control part, infrared fill light part, movement module, etc. Among them, the interface part completes the isolation and protection of the external interface and the conversion of some signals; the power part completes the conversion of AC24V/Hi-PoE power to the power required internally, such as DC12V, DC5V, DC3.3V, etc.; the encoding part mainly completes video compression encoding and network transmission; the pan-tilt control part mainly completes PTZ control; the infrared fill light part mainly completes the driving and switching of the infrared lamp; the movement module is also the core component of the ball machine, completing image acquisition, automatic focusing and zooming of the lens. In order to achieve higher integration and reduce costs, some manufacturers merge the movement module with the encoding part, which is usually called the network movement. Some manufacturers merge the CPU of the pan-tilt control part with the main processor of the encoding part. The entire product has only one processor, which is very integrated and the cost will be lower.

　　This article focuses on the infrared fill light part, but for high-speed balls, the movement is also a key material, so I will briefly mention it. In recent years, with the popularity of high-definition balls, the demand for high-definition movements has increased. The movement prices of international manufacturers are very high, so manufacturers with R&D capabilities have also invested in the research and development of movements, especially high-definition movements. After continuous technical accumulation and development, the technical bottlenecks of most movements have been basically solved, and the products have been launched on the market. Due to the low price and large sales volume, after several years of market use and continuous improvement, whether in terms of ISP processing, focusing, following focus, or long-term stability, it has basically reached the level of international manufacturers, and some indicators and effects have even exceeded those of international manufacturers, and the sales price is low, which has greatly impacted the market leadership of SONY and Hitachi. At the same time, the lens of high-definition movement has also developed rapidly. It is no longer just Japanese manufacturers such as Tamron, Canon, and Fujinon. Domestic manufacturers have also launched a large number of movement lenses, which has greatly promoted the development of movement. Currently, there are roughly two types of movements: digital movements and network movements. Network movements will have greater development in the future and can meet most scenarios with lower costs. Digital movements are suitable for occasions with higher requirements, and the functions of the entire machine can be complete.

　　Infrared fill light technology

　　Monitoring fill light initially used multiple low-power infrared lamps, and then developed array infrared lamps for a period of time. Now most use high-power fill light. High-power fill light includes laser infrared lamp, white light lamp, and high-power dot matrix infrared lamp (Figure 1). The application of laser infrared lamp is mainly synchronous zoom, white light lamp is mainly used in occasions requiring color images, and high-power dot matrix infrared lamp has two main application modes: synchronous zoom and segmented lighting. The following focuses on these two methods.

    Synchronous zoom

　　Synchronous zoom is a function that can achieve synchronous adjustment of the viewing angle and infrared irradiation viewing angle during the zoom process of the infrared ball. The optomechanical and electrical integration mechanism that can achieve this function of adjusting the infrared irradiation angle is called the infrared ball synchronous zoom module, and the specific implementation method is called the infrared synchronous zoom function (Figure 2). The infrared synchronous zoom function can be applied to infrared high-definition ball and infrared high-definition gun camera.

　　Infrared synchronous zoom has the following advantages:

　　The infrared light irradiation angle can be adjusted synchronously with the camera's viewing angle, so that the limited fill light can be more concentrated and the infrared lighting efficiency can be improved;

　　Uniform illumination, eliminating the flashlight effect;

　　Under the same illumination conditions, low power is beneficial to prolong the service life of infrared lamps;

　　Under the same fill light power, the efficiency is higher;

　　Using a small number of high-power lamps, there is no blind spot in the entire zoom range.

　　However, the technical requirements for infrared synchronous zoom research and development are relatively high:

　　It requires coordination of mechanical structure, transmission and optics, and has high requirements for structural design, processing and assembly;

　　The software processing is complex and requires the all-in-one machine to change the magnification and fill light simultaneously;

　　For different movements, it is necessary to conduct a light and image matching test;

　　The optical axis needs to be calibrated during the production of each device, which places high demands on production.

　　Segment lighting

　　The segmented lighting method is to divide multiple high-power dot matrix infrared lamps into 2 or 3 groups. These groups of infrared lamps use spotlight cups with different angles, including large angle, medium angle and small angle. When the movement lens is at different focal lengths, the infrared lamps at different angles are turned on (Figure 3, Figure 4).

    The segmented lighting method has the following disadvantages (Figure 5):

　　There is a problem of insufficient fill light or insufficient focus in the middle section of different magnifications;

　　During the switching process of different groups of lights, the light changes greatly and affects the focus;

　　Some focal lengths have a flashlight effect;

　　Some focal lengths have less light utilization.

　　Of course, the design, production and use of segmented lighting are relatively simple, so many manufacturers are currently using it.

　　Composition of synchronous zoom module

　　The synchronous zoom module consists of an infrared light board, a lens, and a stepper motor. One or more high-power infrared lights are used on the light board. The infrared wavelength can be one of 808nm, 850nm, and 940nm. However, it should be noted that the shorter the wavelength, the closer it is to visible light, and the better the sensor's sensing effect. Therefore, if no red exposure is required, try to use short-wavelength infrared light. The infrared light board is fixed, and there is an optical lens in front of the light. The lens is specially designed and molded, and the optical path matches the infrared light. The distance between the lens and the light can be changed by controlling the rotation of the stepper motor, thereby changing the infrared light's light output angle, achieving a continuous light output angle and evenly distributed light in the picture.

　　In the era of analog monitoring, the first-tier brand movements were mainly SONY and Hitachi, and there were some second-tier brands from South Korea and Taiwan. Later, there were many lower-end analog movement manufacturers in China, but the leading position of SONY and Hitachi has never been changed. Of course, with the development of chip technology, the whole machine of network movement may also develop powerful functions, and the research and development efforts of domestic manufacturers are becoming more and more concentrated, so the future development of movement technology is worth looking forward to.