Abandoning tailing and analyzing the display effect of LCD frequency doubling and frame insertion technology

For a long time, the biggest drawback of LCD TVs is the tailing and blurring of dynamic images. When displaying high-speed images, residual images and tailing are common, so those who like to watch sports channels and fast-paced blockbusters are not very satisfied with the effects of LCD. In order to eliminate this criticism, manufacturers have been seeking technological breakthroughs and trying every means to improve the dynamic display effects of LCD TVs.

The basic technical principle of liquid crystal imaging is to rely on the rotation of the liquid crystal in the liquid crystal panel to control the passage of light to form an image. The rotation of the liquid crystal has a process and requires a reaction time, so there is a lag in the display of moving pictures, which causes the residual image and tailing phenomenon of dynamic pictures. From the perspective of liquid crystal technology, there are two main ways to solve this problem: one is to increase the response time of liquid crystal molecules as much as possible; the other is to reduce the tailing phenomenon to a certain extent by improving the internal circuit processing technology of the TV.

Currently, the shortest response time of LCD TVs has reached 4ms, 2ms or even 1ms, which is basically the bottleneck of current LCD technology. Further increasing the response time of liquid crystal molecules is a very difficult problem. Even shortening it by 1 millisecond is extremely difficult to do. The interpolation technology belongs to the improvement of circuit processing technology and is relatively easy to implement. Currently, TV manufacturers generally use 100/120/240/400Hz and other frequency doubling interpolation technologies.

The so-called frequency doubling interpolation technology is actually a technology that performs frequency doubling interpolation on TV image signals, that is, increasing the original field frequency by interpolating frames. The specific measures can be achieved by "field insertion" technology or "frequency insertion" technology. The former is to insert a black field or gray field without an image into the original image to increase the field frequency, while the latter is to select related points for dynamic point-to-point pixel estimation based on the scene content of the picture and the correlation between the previous and next images, and regenerate an intelligent picture with more accurate brightness, contrast and continuity, and insert it between the previous and next images to double the field frequency.

100Hz/120Hz technology corresponds to PAL/NTSC field frequency respectively. Currently, there are three major TV formats in the world: PAL, NTSC and SECAM. Among them, PAL is the standard format for broadcasting and television in my country and Europe. The standard TV signal format is 25 frames per second. Each frame is scanned by the TV in 2 fields according to odd and even lines. Therefore, the TV needs to scan 50 fields of images in 1 second, that is, 50Hz. In the NTSC format, the TV signal contains 30 frames per second, and the TV restores the image at a frequency of 60 fields per second, that is, 60Hz.

To realize the real 100/120Hz technology, we need to start from both soft and hard indicators. In the development of 100/120Hz technology, simple field doubling, black field insertion, gray field insertion, dynamic GAMMA and other technologies have appeared successively. Strictly speaking, these technologies cannot improve motion blur well, let alone solve the problem of motion jitter.

The 100/120Hz technology currently in use is generally equipped with a proprietary 120Hz LCD screen and ME/MC chip circuit. Through a series of precise calculations, it intelligently generates transition frames, increasing the 50Hz refresh rate of the LCD TV to 100Hz, or increasing the 60Hz refresh rate to 120Hz, thereby effectively improving the afterimage and tailing during the playback of moving pictures, and basically achieving a clear and smooth playback effect.

Although the frequency doubling and interpolation technology still cannot completely eliminate the tailing phenomenon, this type of technology can reduce the animation tailing to a level that is difficult for the human eye to perceive, which actually plays a role in improving the imagination of tailing and residual images. Li Jian, director of the Digital TV Laboratory of the National Radio and Television Product Quality Supervision and Inspection Center, pointed out that the 100/120Hz refresh rate that manufacturers are now vigorously promoting can improve the degree of image jitter and improve image stability. It can indeed play a certain role in improving the dynamic display effect of LCD TVs .