3.4 Special requirements for the screen body of the conference camera
Although the high refresh rate ensures that the large screen can respond in time even when shooting with a high-speed camera, the screen transition and transition are smoother and smoother. However, during use, it will be found that occasionally the camera lens is aligned with the LED display. Inexplicable water waves and strange colors, and with the change of shooting angle, camera lens focal length adjustment, the water ripple will also undergo some changes, which greatly affects the live and recorded display, which is brought by the digitalization of TV cameras. Moiré phenomenon.
If the spatial frequency of the CCD (or CMOS) pixel of the photosensitive element is close to the spatial frequency of the (LED) stripe in the image, moiré is generated. Since the moiré phenomenon is caused by the inherent structure of the LED display, if the condition of the moiré--the grid structure of the LED display or the grid structure of the camera CCD (CMOS) disappears, theoretically Moiré interference can be completely eliminated [3]. The domestic company superimposes an optical processing screen on the surface of the LED display screen. The screen consists of a specific proportion of special light absorbing material and a surface microbead lens coating. Through the use of the optical screen, the LED screen is changed from the original grid-like illumination. Continuous surface illumination, by magnifying the discrete LED pixels, ultimately creates a continuous high-definition image on the surface of the optical processing screen, while maintaining contrast while retaining high definition and eliminating moiré.
4. LED display indoor installation design
4.1 Determine the installation location
The chairman's desk is 15m wide, with side and side curtains on both sides. The display with a width of 12m and a height of 6.2m will not affect the video conference display, nor will it affect the background display of the performance. The product with P3.1 specification can display 1 A full-screen full HD video image can also display 4 HD video images without loss.
The installation position of the screen body is directly related to the optimal viewing distance and viewing angle. GB50464-2008 "Video Display System Engineering Specifications" data and pixel center distance formula H = k ? d. Where H is the maximum line of sight; k is the line of sight coefficient, generally taken 345; d is the character height, and the character is 16 dot matrix Chinese characters. According to the formula, the ideal line of sight H = 345 × 16 × 3.125 = 17.25m; the minimum line of sight is = 1/2 ideal line of sight = 8.6m. Combining the two distances, combined with the application of the podium, the location of the conference area and the location of the TV, it is recommended that the best distance for the first row of directors to view the LED large screen is 18.3m.
According to the visual characteristics of the human eye, the human eye sees the cuboid with a vertical viewing angle of 15° and a horizontal viewing angle of 30°, and is not easy to fatigue. According to the calculation, the first row of the first long distance LED screen is 18.3m, the screen height is 6.2m, the screen width is 12m, the vertical viewing angle is α=16°, and the horizontal viewing angle β is 36.3°. The effect is ideal. The visual calculation is shown in Figure 1 and Figure 2.
It is estimated that the large screen is installed on the podium, the installation space and channel are 5m behind the screen, the front edge of the screen is 12m away from the edge of the podium, and the screen is installed 1.35m away from the ground.
4.2 Installation Basic Design
The large LED display is composed of several boxes. The industry is divided into a simple box and a standard box (also called a waterproof box with a back cover). Outdoor screens are generally made of waterproof cabinets, and simple cabinets are used indoors. After the LED chip is packaged as a pixel, it is arranged on the circuit board according to certain rules, packaged and waterproofed and reinforced to form a module. The module resolution is generally 64×48, and multiple module combinations are packaged in one box. The box unit is formed. Each cabinet unit can be used as a separate display unit for power-on and data display testing. Take a brand product P3.1 as an example. The parameters of the cabinet unit are as follows: size (W×H×D) is 0.4m×0.3m× 0.1m, resolution is 128×96, weight is 5kg (40 kg/m2), flatness is ≤ 0.2mm, peak power consumption is 120W (1000W/m2), and average power consumption is 40W (330W/m2).
4.2.1 Power supply design
The auditorium is an important place and is designed according to the secondary load. The project uses two power sources to supply power at the same time. When a power transformer fault or line fault occurs, the power supply will not be interrupted, and the other power source can bear the full load. According to the "Technical Specifications for Video Display System Engineering", combined with the design parameters of the factory, the LED display is fully loaded with electric power, calculated at 1000W per square meter. The main screen, auxiliary screen and monogram screen have a total load of 110 kW and an average power of 36.3 kW. According to the LED power supply design safety specification, the power supply power should be designed with a margin. The power of the general power supply = the power of the LED × 1.2, the total power consumption of the LED display in the project is 132kW.
The ability of LED devices to withstand surges is relatively poor, especially against reverse voltage. In the design of the power supply, the first is to design a smart distribution box, which can monitor the load operation of the entire LED display in real time. The second is to install UPS or purify the power supply at the front end of the power distribution. The third is to plan the power line reasonably. The power configuration of the project takes into account the power factor and optimum operating efficiency of the UPS. The rated power of the UPS is 132/0.8=165kV · A, and the power supply model is GES-NT 160kV · A modular UPS. Install 160 kV · A UPS and battery cabinet (reserve time 0.5h) in the underground power distribution room, and connect 120mm24+1 cable from the main distribution bus copper pressure line to the UPS input and output power distribution cabinet 350A. Directly connected to the UPS input, the UPS output is connected to the UPS input and output power distribution cabinet 300A, and the lower 90mm24+1 cable is connected to the LED large-screen intelligent distribution box.
4.2.2 Cabinet installation
The LED display box has an iron box, an aluminum box and a die-cast aluminum box. The three cabinets are used in different applications. Die-cast aluminum box is mainly used for high-end and lease. Its characteristics are: modular, simple connection, no fan cooling, ultra-quiet, good effect. This project uses die-cast aluminum box. The installation and maintenance bracket of the box is 12m wide, 6.85m high and 0.8m deep. The weight of the main screen box is 2 976kg. The weight of the box maintenance bracket is about the same as the weight of the box. The total weight of the whole screen is 6t and the load-bearing area is 9.6. M2 (12m × 0.8m), weighing 625kg per square meter, because there is no basement under the stage to support the column, so we need to install a 12m × 1.2m load-bearing foundation under the LED screen to expand the bearing area. The weight of the auxiliary screen is 480kg. There is a beam in the middle of the ear wall, and the filling part is a hollow brick. The load-bearing frame is first installed on the beam, and then the box is fixed to the frame.
The LED display steel structure frame shall be constructed in strict accordance with the confirmed design drawings, "Code for the Acceptance of Construction Quality of Steel Structure Engineering" (GB 50205-2001) and other current construction acceptance specifications, frame, support frame and display box The product components such as the controller box should be installed firmly, the structure is stable, the corner transition is smooth, no flash, no burrs, various fixing bolts are fastened, and the metal components need to be well grounded. In the north, the static electricity of the human body and the static electricity of the circuit will bring accidental damage to the LED display. It is necessary to reliably realize the working grounding, connect the equipotential of the digital circuit to the earth, and establish a static charge discharge channel of the LED display system.
4.3 System Installation and Debugging
The development of LED displays to small-pitch, high-density TV screens, physical pixel spacing is not a major factor limiting the clarity of the display, and can not replace the definition with high display resolution. The definition of the display is a subjective feeling of the human eye on the resolution, uniformity, brightness, contrast and other factors of the display screen. To achieve the consistency of subjective feelings, the performance parameters of the LEDs must first be consistent. This is based on the pre-component screening and LED parameter subdivision, and the subsequent accurate correction.
4.3.1 Screen pixel brightness and chromaticity uniformity requirements
In the production and manufacturing aspects, the uniformity of the LED parameters will have different effects. At the same time, after the faulty board is replaced, obvious bright areas will appear without adjustment; in order to make various display images smooth, true color reproduction, and uniform brightness, It is necessary to adjust the point-by-point luminance and chromaticity uniformity of a specific pixel in a specific area.
4.3.2 Color reproduction technical requirements
At present, various LED display technologies generally adopt RGB as the three primary colors, but the color coordinates corresponding to the three primary colors are not completely the same. Some products have the problems of high color saturation and incomplete color gamut, and need to strictly follow the color theory. Strong and color coordinate correction ensures that the ideal pure color is displayed for dynamic white balance of the display.
4.3.3 Fast motion image compensation technology
The LED display screen is displayed in a progressive manner, and the video signal of the camera is interlaced. In the interlaced to progressive conversion, different processing methods should be adopted for the still picture and the moving picture to ensure the definition of the still picture. Remove the smearing of motion pictures.
4.3.4 Single Point Correction Technology
The single-module brightness and chromaticity correction technology can correct the brightness and chromaticity of a single module. This technology solves the problem of chromatic aberration between the new module and the old module after the screen is replaced. The single-point calibration system individually controls each pixel in each display panel, including its brightness and color control, to achieve unprecedented uniformity and produce the sharpest image. At the same time, in order to improve the color reproduction degree and reduce the attenuation and distortion of the image during processing and transmission, it is also necessary to select a reliable image processor and a fiber optic transmitter.
5. Conclusion
This paper comprehensively introduces the design method of indoor LED display screens from the aspects of dot pitch selection, pixel packaging, line of sight determination, circuit design, installation foundation and system debugging. Precautions can improve the planning and design capabilities of indoor LED displays for practitioners, and have a great impetus to the application of LED displays indoors.
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