LED electronic display has good pixels, no matter day or night, sunny or rainy days, LED display can let the audience see the content, to meet people's demand for display system.
Image acquisition technology
The main principle of LED electronic display is to convert digital signals into image signals and present them through the luminous system. The traditional method is to use video capture card combined with VGA card to achieve display function. The main function of video acquisition card is to capture video images, and obtain the index addresses of line frequency, field frequency and pixel points by VGA, and obtain digital signals mainly by copying the color lookup table. Generally, software can be used for real-time replication or hardware theft, compared with hardware theft is more efficient. However, the traditional method has the problem of compatibility with VGA, which leads to blurred edges, poor image quality and so on, and finally damages the image quality of electronic display.
Based on this, industry experts developed a dedicated video card JMC-LED, the principle of the card is based on PCI bus using 64-bit graphics accelerator to promote VGA and video functions into one, and to achieve the video data and VGA data to form a superposition effect, the previous compatibility problems have been effectively solved. Secondly, the resolution acquisition adopts the full-screen mode to ensure the full Angle optimization of the video image, the edge part is no longer fuzzy, and the image can be arbitrarily scaled and moved to meet different playback requirements. Finally, the three colors of red, green and blue can be effectively separated to meet the requirements of true color electronic display screen.
2. Real image color reproduction
The principle of the LED full-color display is similar to that of the television in terms of visual performance. Through the effective combination of red, green and blue colors, different colors of the image can be restored and reproduced. The purity of the three colors red, green and blue will directly affect the reproduction of the image color. It should be noted that the reproduction of the image is not a random combination of red, green and blue colors, but a certain premise is required.
First, the light intensity ratio of red, green and blue should be close to 3:6:1; Secondly, compared with the other two colors, people have a certain sensitivity to red in vision, so it is necessary to evenly distribute red in the display space. Thirdly, because people's vision is responding to the nonlinear curve of the light intensity of red, green and blue, it is necessary to correct the light emitted from the inside of the TV by white light with different light intensity. Fourth, different people have different color resolution abilities under different circumstances, so it is necessary to find out the objective indicators of color reproduction, which are generally as follows:
(1) The wavelengths of red, green and blue were 660nm, 525nm and 470nm;
(2) The use of 4 tube unit with white light is better (more than 4 tubes can also, mainly depends on the light intensity);
(3) The gray level of the three primary colors is 256;
(4) Nonlinear correction must be adopted to process LED pixels.
The red, green and blue light distribution control system can be realized by the hardware system or by the corresponding playback system software.
3. special reality drive circuit
There are several ways to classify the current pixel tube: (1) scan driver; (2) DC drive; (3) constant current source drive. According to different requirements of the screen, the scanning method is different. For indoor lattice block screen, scanning mode is mainly used. For outdoor pixel tube screen, in order to ensure the stability and clarity of its image, DC driving mode must be adopted to add a constant current to the scanning device.
Early LED mainly used low-voltage signal series and conversion mode, this mode has many solder joints, high production cost, insufficient reliability and other shortcomings, these shortcomings limited the development of LED electronic display in a certain period of time. In order to solve the above shortcomings of LED electronic display, a company in the United States developed the application-specific integrated circuit, or ASIC, which can realize the series-parallel conversion and current drive into one, the integrated circuit has the following characteristics: the parallel output driving capacity, driving current class up to 200MA, LED on this basis can be driven immediately; Large current and voltage tolerance, wide range, generally can be between 5-15V flexible choice; The serial-parallel output current is larger, the current inflow and output are greater than 4MA; Faster data processing speed, suitable for the current multi-gray color LED display driver function.
4. brightness control D/T conversion technology
LED electronic display is composed of many independent pixels by arrangement and combination. Based on the feature of separating pixels from each other, LED electronic display can only expand its luminous control driving mode through digital signals. When the pixel is illuminated, its luminous state is mainly controlled by the controller, and it is driven independently. When the video needs to be presented in color, it means that the brightness and color of each pixel need to be effectively controlled, and the scanning operation is required to be completed synchronously within a specified time.
Some large LED electronic displays are composed of tens of thousands of pixels, which greatly increases the complexity in the process of color control, so higher requirements are put forward for data transmission. It is not realistic to set D/A for each pixel in the actual control process, so it is necessary to find a scheme that can effectively control the complex pixel system.
By analyzing the principle of vision, it is found that the average brightness of a pixel mainly depends on its bright-off ratio. If the bright-off ratio is effectively adjusted for this point, the effective control of brightness can be achieved. Applying this principle to LED electronic displays means converting digital signals into time signals, that is, the conversion between D/A.
5. Data reconstruction and storage technology
At present, there are two main ways of organizing memory groups. One is the combination pixel method, that is, all pixel points on the picture are stored in a single memory body; the other is the bit plane method, that is, all pixel points on the picture are stored in different memory bodies. The direct effect of multiple use of storage body is to realize a variety of pixel information reading at a time. Among the above two storage structures, the bit plane method has more advantages, which is better in improving the display effect of LED screen. Through data reconstruction circuit to achieve the conversion of RGB data, the same weight with different pixels is organically combined and placed in the adjacent storage structure.
6. ISP technology in logic circuit design
The traditional LED electronic display control circuit is mainly designed by conventional digital circuit, which is generally controlled by digital circuit combination. In traditional technology, after the circuit design part is completed, the circuit board is made first, and the relevant components are installed and the effect is adjusted. When the circuit board logic function cannot meet the actual demand, it needs to be remade until it meets the use effect. It can be seen that the traditional design method not only has a certain degree of contingency in effect, but also has a long design cycle, which affects the effective development of various processes. When components fail, maintenance is difficult and the cost is high.
On this basis, system programmable technology (ISP) appeared, users can have the function of repeatedly modifying their own design goals and the system or circuit board and other components, realizing the process of designers' hardware program to software program, digital system on the basis of system programmable technology take on a new look. With the introduction of system programmable technology, not only the design cycle is shortened, but also the use of components is radically expanded, field maintenance and target equipment functions are simplified. An important feature of system programmable technology is that it does not need to consider whether the selected device has any influence when using system software to input logic. During input, components can be selected at will, and even virtual components can be selected. After input is completed, adaptation can be carried out.
Post time: Dec-21-2022
