TV programs are becoming more and more colorful, more and more interactive, and the visual impact on viewers is also increasing. Among them, the background of the program plays an important role. In recent years, LED display screens and DLP splicing screens have gradually become the mainstream of the program background. This article intends to do some analysis and discussion on the technical characteristics, use effects, advantages and disadvantages and precautions of these two display screens.
1. LED display
LED is the abbreviation of LightEmittingDiode, which means light emitting diode in Chinese. It is a solid-state semiconductor device that can directly convert electrical energy into light energy. LED display is an advanced digital information product. It successfully integrates computer technology, network communication technology, image processing technology, embedded control technology, etc., with flexible display area and resolution (modular can be arbitrarily assembled), high Brightness, low power consumption, long life, low heat, environmental protection and other advantages, comprehensive use of sound, light, electricity, graphics, text, is a comprehensive and perfect terminal product for displaying information.
LED display screens are more and more used in large-scale events broadcast in TV studios and TVs. As a stage background, it provides a variety of vivid and dazzling background pictures and more interactive functions, making the background pictures also dynamic and static To make the performance and the background one, making people feel immersive. It brings more space for imagination to the dancers, designing a modern and visually striking stage, perfectly blending the atmosphere of the scene and the program, and achieving functions and effects that are difficult to achieve with other stage art equipment.
The audience's viewing effects and feelings on the LED display screen are very intuitive. As long as the screen size and pixel spacing and viewing distance are appropriate, this direct-view display screen can obtain excellent results. However, the number of viewers in front of the TV set is much larger than the number of on-site viewers. Therefore, the viewing effect of the viewers in front of the TV set is the focus of research and discussion by TV technicians. Many stations use LED display screens, but the effect of the TV screens varies greatly.Some of the pictures are bright, clear and stable from the beginning to the end; some are small and indistinct when viewed from a distance, or are the highlights of some activities when they are near The erratic fringe interference often appears in close-up shots of some characters, which disturbs the audience's sight.
Pay attention to the following aspects in the selection and use of LED display:
1. Point spacing should be as small as possible
The dot pitch is the distance between the center points of adjacent pixels of the LED display. The smaller the dot pitch, the more pixels per unit area, the higher the resolution, the closer the shooting distance, of course, the more expensive the price. At present, the dot pitch of LED display screens used in domestic TV studios is mostly 6-8 mm.In order to achieve excellent results, we must carefully study the relationship between the resolution of the signal source and the dot pitch, and strive to achieve consistent resolution. Achieve point-to-point display to achieve the best results.
2. Higher fill factor
The fill factor (FillFactor) of the LED display screen is also called the bright area ratio, that is, the ratio of the light emitting area of each pixel to the physical surface area occupied by the pixel. The LED display screen is made up of discrete pixels, and there are obvious non-luminous black areas between the pixels. When viewed at close range, the picture is incoherent and incomplete, and uneven brightness produces a grainy feeling.If the light source is limited to a small pixel surface area, resulting in the brightness of a single pixel being several times or even more than ten times the brightness of the entire screen, Causes a more serious dazzling feeling. The TCO’99 standard recognized by the flat panel display industry stipulates that the fill factor should not be less than 50%. At present, the fill factor of many LED displays on the market has not reached this index. The cut-off characteristic of the TV's low-pass filter also directly affects the appropriate shooting distance of LED display screens with different fill factors.
For LED display screens with the same dot pitch, the smaller the fill factor is, the more the attenuation factor is. There is more attenuation, so the shooting distance needs to be increased. If the system low-pass filter passband is 4MHz and the high-frequency attenuation characteristic is 12db / octave, then the shooting distance with a fill factor of 25% is attenuated by 1.15db more than the fill factor of 50%, and the shooting distance needs to be increased by about 10 %. The increase of the fill factor makes the display's viewing angle wider and the color mixing effect more ideal. It overcomes the dazzling problem of pixels and also creates conditions for properly increasing the brightness of the entire screen to obtain better results. Jiangsu Education Station chose an LED display with a fill factor of 60%. It has moderate and soft brightness, uniform and bright colors, and clear and delicate expression, ensuring the high quality of the display screen.
3. Color temperature can be adjusted
Color temperature (ColorTemperature) is the temperature determined by comparing the shape of the emission spectrum of the emitter with the shape of the best-fit black body emission spectrum. When the LED display screen is used as the background in the studio, its color temperature should be consistent with the color temperature of the lights in the studio to obtain accurate color reproduction in the shooting. According to the needs of the program, the lighting of the studio sometimes uses 3200K low color temperature lamps and sometimes 5600K high color temperature lamps. The LED display screen needs to be adjusted to the corresponding color temperature to obtain satisfactory shooting results.
4. The shooting distance should be appropriate
As mentioned before about the dot pitch and fill factor, the appropriate shooting distance is different for LED displays with different dot pitch and different fill factors. The distance between the person being photographed and the screen is more suitable at 4-10 meters, so that when shooting people, you can get a better background picture. If the person is too close to the screen, the background will appear grainy when shooting close-up shots, and it is also prone to moire.
5. Ensure a good environment
During the service life of the product, the failure rate is low only under suitable working conditions. As an integrated electronic product, the LED display is mainly composed of a control board equipped with electronic components, a switching power supply, a light emitting device, etc., and the life and stability of all these components are closely related to the operating temperature. If the actual operating temperature exceeds the specified range of use of the product, not only its life will be shortened, but the product itself will also be severely damaged. In addition, the threat of dust cannot be ignored. Working in a relatively dusty environment, because the PCB adsorbs dust, and the deposition of dust will affect the heat dissipation of electronic components, will cause the temperature of the components to rise, and then the thermal stability will decline or even leakage will occur. In severe cases, it will cause burnout. Dust also absorbs moisture, which corrodes electronic circuits, causing short-circuit problems that are difficult to troubleshoot. Pay attention to keeping the studio clean. The transformation of the studio will produce a lot of dust, and the LED display screen needs to be protected in advance.
The use of LED display screen greatly enriches the display form of the program background. The LED display screen is suitable for large-scale variety shows in large scenes and large studios.
2. DLP splicing screen
DLP is the abbreviation of DigitalLightProcessing, which means digital light processing in Chinese. This technology is to process the image signal first and then project the light. From the technical principle of DLP, it has the advantages of least signal noise, accurate gray level, high reflectivity, seamless image display, high reliability and so on. The DLP splicing screen is formed by splicing multiple rear projection display units. Its main feature is the small stitching, which can be controlled to less than 0.5 mm. Everyone calls it "seamless" splicing, which is also the other two major technical LCDs. And PDP can not reach. Due to its advantages, in recent years, TV stations have used DLP splicing screens as the background of the studio. CNN, BBC, SKY, CCTV and other well-known big TV stations have achieved very good program results after use.
DLP splicing screens also have disadvantages. Because the light source of DLP splicing is from the light bulb, it has large power consumption and high heat dissipation, and the brightness will decrease after a period of use. The user must constantly replace the light bulb to maintain the original display effect. With the development of technology, thanks to the addition of LED light sources, the current DLP splicing screen has solved a series of problems such as frequent lamp replacement, large power consumption, and high heat dissipation. After adopting the LED light source, the DLP splicing screen not only has a big breakthrough in service life and power consumption, but also has a revolutionary change in color, so that the DLP splicing screen continues to maintain its market leading advantage.
In order to achieve satisfactory TV effects, we should pay attention to the following aspects in the selection and use of DLP splicing screens:
1. The stitching gap should be as small as possible
The effect of the background display we want on the TV is seamless, which requires the stitching gap to be small enough so that the gap cannot be seen from the lens. At present, the use of titanium alloy needle suture technology can reduce the splicing gap to less than 0.2 mm, and at the same time, the design of the connecting plate can ensure that the screen does not deform during thermal expansion and contraction, providing high-quality image geometry and sharpness for the entire screen .
2. High uniformity
The DLP splicing screen is composed of multiple display screens, which also causes individual differences in each screen, and we hope that they look like a large display screen with matching colors and brightness, which needs to be improved by technical means. Uniformity. At present, this technology is relatively mature, and advanced manufacturers have been able to operate in the background silent mode without operator involvement.It integrates a proprietary brightness and color sensor to continuously measure the color and brightness of the screen wall and between the projection modules Communicate, automatically match all white, all black and all gray level brightness and all display module colors between the two, and keep the gray level of the entire display screen the same, thus achieving long-term consistency of images under multi-screen stitching.