(1) Synchronization of certificate output to avoid asynchrony of splicing pictures;
(2) Optimize the image processing algorithm to keep the zoomed image with high definition;
(3) Customize the output resolution to deal with the irregular physical resolution of the LED display.
Small pitch LED display
2. Splicing processing technology applied to small-pitch LED displays
2.1 The use of splicer and small-pitch LED display
A key application of the splicer is that it can output multiple DVI signals to splice and display multiple display screens arranged in a matrix, making it a logically complete display area.
For the LED display, we can define the display area driven by an LED controller as an independent LED display. The current LED controller uses DVI/HDMI as the signal input interface and supports the maximum input resolution of 1920×1200@60Hz, the maximum bandwidth is 165MHz, and the maximum physical resolution of the driven LED display is 1920×1200.
As the display area of LED small-pitch products becomes larger and larger, projects of tens of square meters are not uncommon. The physical resolution of LED displays tends to exceed 1920×1200, that is, each ultra-large-scale LED display consists of several It is composed of several independent display areas driven by one LED controller. For splicer applications, it only needs to provide several DVI output interfaces corresponding to the number of LED controllers, and splice and display the entire LED screen.
In the application of splicers in small-pitch LED displays, there are several key technologies worthy of attention:
(1) The output synchronization of the signal
The multi-channel DVI signal output of the splicer must have the problem of signal synchronization. When the unsynchronized signal is output to the LED display, the picture tearing phenomenon will appear at the splicing place, which is especially obvious when playing high-speed moving images. How to ensure the output synchronization of the signal has become the key to measuring the success or failure of a splicing system.
(2) Graphics processing algorithm
We know that the point-to-point image display effect is the best. After the reduced image, if only ordinary graphics processing technology or general FPGA graphics processing algorithms are used, the edges of the image will appear jagged, and even pixels will be missing. The brightness will also decrease. And high-end image processing chips or FPGA systems using complex graphics processing algorithms will ensure the display effect of the reduced image to the utmost extent. Therefore, a good graphics processing algorithm is a key technology for splicers applied to small-pitch LED display screens.
(3) Output of non-standard resolution
The small-pitch LED display is composed of a matrix of display units of the same specification. The size and physical resolution of each display unit are fixed, but the spliced entire large screen is often not a standard physical resolution. For example, the resolution of the display unit is 128×96, which can only spell 1920×1152, but it cannot spell 1920×1080. In a super large-scale splicing system, the LED display area driven by each LED controller may not be of standard resolution. At this time, it is critical that the splicer has a non-standard resolution output, which can help us quickly find a suitable one. The splicing method can allocate resources reasonably and effectively save the number of LED controllers and transmission equipment.
2.2 Splicers applied to small-pitch LED displays
At present, splicers can be divided into four categories, namely, embedded pure hardware architecture, PCI-E bus architecture, distributed network architecture, and hybrid architecture.
(1) Embedded pure hardware architecture
The structure of the whole machine usually adopts the design of "backplane + signal acquisition board + main control board + signal output board". The signal acquisition board performs signal processing such as video acquisition, scaling, superposition, and format conversion. The processed signal is transmitted to the FPGA signal processing system of the main control board, and functions such as configuration of the main control FPGA, communication with the upper PC, and data exchange between systems are realized through the embedded ARM system, and the signal is output to the display terminal through the signal output board .
The structure of the pure hardware architecture splicer is relatively simple, and it is not prone to system failure; the acquisition board and output board can be hot-swapped and easy to replace; it can realize the acquisition and processing of multi-channel and multi-format signals; backplane exchange technology and output board The card unified clock technology ensures the synchronization of multiple signal outputs; the resolution of each DVI output signal can be customized, which conforms to the splicing characteristics of LED displays.
Many features make the pure hardware architecture quickly become one of the mainstream products in the splicer field today. However, due to the use of FPGA as the core image processing unit, the quality of the algorithm determines the processing effect of a splicer, especially the image scaling algorithm. How to optimize to achieve a clearer display effect has become a judgment An important indicator of the value of pure hardware splicing devices.
(2) PCI-E bus architecture
Usually the splicer of the bus architecture adopts PCIExpress technology, and the available data bandwidth is as high as hundreds of Gbps. The host is equipped with high-performance CPU and large-capacity memory. Different operating systems (such as 64-bit Windows 7) can be pre-installed according to different application fields, and various applications can be run directly. The splicer is equipped with multiple high-performance graphics output cards, each of which has ultra-high internal bandwidth and video memory, and all output images are synchronized to eliminate image tearing between display units. It is also equipped with multiple input cards, supports multiple signal formats, and can perform image processing on input signals.
The PCI-E bus architecture splicer is a high-performance computer. All components use the most advanced and mature technologies of major hardware manufacturers. For example, Intel can be used for CPU, and Nvidia can be used for graphics card. All high and new technologies in the computer field can also be quickly integrated. This makes the PCI-E bus architecture splicer has incomparable advantages in terms of computing speed, image processing, and operating methods.
The PCI-E bus architecture splicer has a very low threshold. For simple applications, an industrial computer plus a professional multi-channel output graphics card can be realized.
On the other hand, how to solve the problem of system stability, how to design an intuitive and powerful control software, how to solve various problems of data transmission under high bus bandwidth, etc., all require a strong R&D team and a strong financial foundation. Need to accumulate experience. In other words, high-end PCI-E bus architecture splicers not only need to meet the most basic applications such as signal acquisition, processing, and splicing, but also require more investment in the design of system stability and software ease of use. The splicer can meet various harsh application environments.
However, it should be noted that most of the bus architecture splicers use Windows operating system. Once they are attacked by viruses, the system may be paralyzed and the display will stop. Moreover, due to the use of customized graphics cards, the resolution of each output channel generally needs to comply with the VESA (Video Electronics Standards Association) standard, and it is not possible to define non-standard resolution output, nor to define a different resolution for each channel.
(3) Distributed network architecture
Distributed network architecture splicers usually adopt a node-type hardware structure, and each input and output node is independently separated, and is connected to the central switch through a twisted pair to perform interactive transmission of data.
Its core is a set of advanced video coding and decoding technology. Through various signal input nodes, the collected DVI, VGA, YPbPr, CVBS, 3G-SDI and other signals are processed and coded, and the code is coded through a dedicated network communication protocol. The subsequent video stream is transmitted through the central switch to the output node for decoding, and converted into a DVI digital signal for output to the display terminal.
The synchronization of output nodes has become the key to the application of this system. One way is to send the synchronization code directly through the network to realize the synchronous output of multiple output nodes. However, due to the existence of the network error rate, after running this mode for a period of time, the output will still be out of sync. Another method is to physically connect multiple output nodes through the SYNC interface, select one output node as the host, and actively send synchronization codes to other output nodes, so that all output nodes receive synchronization signals at the same time, realizing true frame synchronization Output to ensure that the displayed image is complete and there is no tearing at the screen splicing.
At present, there are more and more applications of the splicing system of distributed network architecture. Due to its distributed characteristics, it is convenient for the integrated wiring of the entire building and the centralized management of multiple display terminals in different areas. With the help of advanced visualization software, it can provide users with humanized, visualized and integrated services.
However, limited by bandwidth and codec technology, the distributed network architecture currently does not support the access of dual-link DVI digital signals and HDMI signals. At the same time, since encoding, processing, decoding, and signal synchronization output all require frame buffering, there is a gap in data real-time performance compared with other splicing technologies. In addition, when the number of points to be displayed exceeds 1920×1200 resolution images (two or more signal input nodes are required), the resynchronization output of the input signals of multiple synchronization sources cannot be guaranteed.
(4) Hybrid architecture
Hybrid architecture generally refers to a splicer or splicing system that combines two or more of the above three splicing technologies.
For example, PCI+ hardware backplane bus architecture splicer, its system control and image processing are implemented independently. The PCI bus is responsible for system control and the operating system runs in the background; the hardware backplane bus is responsible for video image processing. The system allows simultaneous processing of a large number of high-resolution input signals while still maintaining real-time operating performance and performance at full frame rate. The best image quality, while ensuring the synchronization of the output signal. For important emergency places, it can ensure that the screen will never be black. Even if the operating system responsible for the PCI bus fails or is infected by a virus, the dedicated backplane graphics processing bus can ensure that external video images are displayed at any time.
Through the hybrid architecture, it is possible to integrate applications, learn from each other's strengths, and greatly increase the stability of the system. This is also the development direction of splicing technology in the future, with a broader application space.
3. Application of small-pitch LED display
At present, small-pitch LED displays are widely used, including but not limited to:
Military exercise command system
Public safety display command system
Power Dispatching System
Traffic road network and aviation monitoring display system
Energy industry production scheduling system
Government and enterprise conference display system
Broadcasting and television media display system
Public Place Information Issuing System
As a new generation of background wall display terminals, small-pitch LED displays are providing high-quality services for key systems in all walks of life.
