Processing method of video signal for large LED screen
The LED screen is a digital flat panel display. This requires that it can display various information such as text, graphics, animation, images, and video programs. The purpose of the full-color LED screen is to create a giant color display. Large LED screens have many similarities to flat panel displays such as plasma displays and large rear projection TVs.
In contrast, LED may be more difficult than other flat panel displays in terms of data distribution, driving, reducing power consumption, improving efficiency, color retention and consistency. This is because light-emitting diodes are non-irritating devices, the switching time is nanoseconds, and there is no memory function. In addition, it has a large display area and a long signal transmission distance, so it cannot use the most advanced large-scale integrated circuits such as COG and SOB. The following is a brief introduction to the processing of the image signal by the LED display.
There are generally two methods for LED screens to process image signals:
One method is to use a dedicated large-screen signal processor to convert the interlaced TV signal into a progressive signal after processing, and then play it on the large screen. The high-performance processor can handle more than 10 bits, and interpolation operations, motion prediction and compensation, and scan conversion must be performed during scan conversion. Now high-end large-scale LED screens also adopt this method, and carry out more image signal processing, trying to upgrade the signal to the broadcast level, and of course the effect is better. Computer images are also processed by this processor, and then sent to a large screen for display. Processing technology is still developing, and many new algorithms have been proposed. We are familiar with large-size rear-projection TVs and large-screen plasma TVs that use this method extensively, and the effect is much better than ordinary TVs. In this case, the output signal is usually described according to the transformed signal format, which is more accurate.
Another method is the multimedia method, commonly known as the synchronous screen method, which uses an ordinary multimedia card to capture the TV signal, and performs demodulation, filtering, and timbre separation. After the image signal is converted by A/D, it is encoded and compressed by MPEG for storage. It is then decompressed during playback and viewed directly on a computer monitor. The signal sent to the large screen is obtained from the computer’s DVI interface or graphics card through a dedicated adapter card, and some processing is required on the adapter card. At this time, the large screen is actually equivalent to the computer monitor or a part on it, usually called a window, which can realize synchronous display of one-to-one correspondence. Since the computer monitor is progressively scanned, if there is no frame extraction processing for the display signal, then the display format of the large screen is the format of the monitor.
For example, the VGA format is a progressive scan format with a pixel count of 640×480 and a scan update rate of 75Hz. However, the 75Hz progressive scan signal here is not an improvement of the image source itself, and the image quality has not improved. In fact, it is even worse than the 50Hz interlaced scan signal, similar to the effect of DVD or VCD, which is often confused The place. As for some screens, the screens have been replaced, for example, the even-numbered screen information is discarded and only the odd-numbered screen information is sent for display. Of course, the effect is even worse. By the way, the situation of non-image programs is relatively simple. Although some game animations also require good continuity, for animations played on large screens, a frame update rate exceeding 10Hz is acceptable.
The display screen is controlled by an embedded controller or a single-chip microcomputer, and the program is generated by the controller. Due to the limitation of the processing capacity of the controller, the speed of providing the picture is not fast enough, which will cause the picture to be discontinuous. The most typical phenomenon is that when the text is moved left or right on the bar screen controlled by the microcontroller, it is not smooth but jumpy. It can be concluded from experience and calculation that if a bar screen composed of 10 16XI6 dot matrix Chinese characters needs to move to the left at a speed of 5 seconds, its frame frequency must reach more than 15Hz in order to move smoothly and coherently.