TV programs are becoming more and more colorful, more and more interactive, and the visual impact on the audience is also increasing, in which the background of the program plays an important role. In recent years, LED displays and DLP splicing screens gradually become the mainstream of the program background, this paper intends to do some analysis and discussion on the technical characteristics, use effects, advantages and disadvantages, and precautions of these two displays.
First, the LED display
LED is an abbreviation for LightEmittingDiode, Chinese meaning light-emitting diode, and is a solid-state semiconductor device that directly converts 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 and changeable display area and resolution (modular can be arbitrarily assembled), high brightness, low power consumption, long life, low heat, environmental protection and durability, and other advantages, comprehensive use of sound, light, electricity, graph, text, is a comprehensive, perfect display of information terminal products.
LED display is increasingly used in TV studios and large-scale events of TV broadcasting, as a stage background, it provides a variety of vivid, dazzling background pictures and more interactive functions, so that the background screen is also moving and quiet so that the performance and the background are integrated so that people have an immersive feeling. It brings a greater space for reverie to the stage, designs a modern and visually impactful stage, perfectly integrates the atmosphere of the scene and the program, and realizes the functions and effects that are difficult to achieve with other stage art equipment.
The viewing effect and feeling of the audience on the LED display is very intuitive, as long as the screen size and pixel spacing, and viewing distance are appropriate, this direct-looking display can obtain excellent results. However, the number of viewers in front of the TV is much greater than the number of live viewers, so the viewing effect of the audience in front of the TV is the focus of research and discussion by TV technicians. Many units use LED displays, but the TV picture effect is very different, and some of the pictures are bright and clear, and stable from beginning to end; Some are small and unclear when the picture is small in the distance, and the close-up scene is either the highlight of some activities or the fluttering stripe interference, in some close-up shots of people, there is often a network interference, disturbing the audience’s line of sight.
In the selection and use of LED display process should pay attention to the following aspects:
1. The point spacing should be as small as possible
The point spacing is the distance between the center points of adjacent pixels of the LED display. The smaller the point spacing, the more pixels per unit area, the higher the resolution, the closer the shooting distance can be, of course, the more expensive it is. At present, the point spacing of the LED display used in the studio of domestic television stations is mostly 6-8 mm, in order to achieve excellent results, it is necessary to carefully study the relationship between the resolution of the signal source and the point spacing, and strive to achieve the same resolution, to achieve point-to-point display, so as to achieve the best results.
2. The filling factor should be high
The fill factor (FillFactor) of the LED display is also known as the light zone ratio, that is, the ratio of the luminous area of each pixel to the physical surface area occupied by the pixel. LED display is arranged by discrete pixels, and there is a clear non-illuminating black area between the pixels. When viewed closely, the picture is incoherent and incomplete, and the brightness is uneven to produce graininess, if the luminous source is limited to a small pixel surface area, resulting in a single pixel brightness several times or even more than ten times the brightness of the whole screen, it will cause a more serious sense of glare. The TCO’99 standard recognized by the flat panel display industry stipulates that the filling factor should not be less than 50%. The filling coefficient of many LED displays on the market does not reach this indicator. The cutoff characteristics of the TV’s low-pass filter also directly affect the appropriate shooting distance for LED displays with different fill coefficients.
For LED displays with the same point spacing, the small filling coefficient is more attenuated than the large filling coefficient, so the shooting distance needs to be increased. If the system has a low-pass filter passband of 4MHz and a high-frequency attenuation characteristic of 12db/octave, then the shooting distance with a fill factor of 25% is 1.15db more than the attenuation of 50% of the fill factor, and the shooting distance needs to be increased by about 10%. The improvement of the filling coefficient makes the viewing angle of the display more extensive, the color mixing effect is more ideal, overcomes the glare problem of pixels, and also creates conditions for appropriately improving the brightness of the whole screen to obtain better results. Jiangsu Education Station has selected an LED display with a filling factor of 60%, which has moderate soft brightness, uniform and bright colors, and clear and delicate expression, which ensures the high quality of the display screen.
3. The color temperature can be adjusted
color temperature is the temperature determined by comparing the emitter emission spectral shape to the best-fitting blackbody emission spectral shape. When the studio uses the LED display as the background, 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, sometimes uses 5600K high color temperature lamps, and the LED display needs to be adjusted to the corresponding color temperature, so as to obtain a satisfactory shooting effect.
4. The shooting distance should be appropriate
As mentioned earlier about point spacing and filling coefficient, LED displays with different point spacing and different fill factors are not the same for the appropriate shooting distance. The distance between the photographed person and the screen is more suitable at 4-10 meters so that you can get a better background picture when shooting the character. If the person is too close to the screen, when shooting a close-up scene, the background will appear grainy, and it is easy to produce network interference.
5. Ensure a good environment for the use
The product’s failure rate is low only under the right operating conditions during the product’s service life. LED display is an integrated electronic product, it is mainly composed of electronic components equipped with control boards, switching power supplies, light-emitting devices, 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 will its life be shortened, but the product itself will also be seriously damaged. In addition, the threat of dust cannot be ignored. Working in a relatively large dust environment, due to the PCB adsorption of dust, and the deposition of dust will affect the heat dissipation of electronic components, which will lead to a rise in the temperature of the components, and then the thermal stability will decline or even produce leakage, which will lead to burn-out when serious. Dust also absorbs moisture, which corrodes electronic circuits and causes some short-circuit problems that are not easy to detect. Be careful to keep the studio clean. Studio renovation will generate a lot of dust, and it is necessary to protect the LED display in advance.
The use of LED display has greatly enriched the display form of the program background, and the LED display screen is used as the background, which is suitable for large-scale variety shows with large scenes and large studios.
Second, the DLP splicing screen
DLP is an abbreviation for DigitalLightProcessing, Chinese means digital light processing, this technology first digitally process the image signal and then projects the light out. From the technical principle of DLP, it has the advantages of minimum signal noise, accurate gray level, high reflectivity, seamless image display, and high reliability. DLP splicing screen by a plurality of rear projection display unit splicing, its main feature is that the seam is small, and can be controlled to 0.5 mm or less, everyone calls it “seamless” splicing, which is also the other two major technology LCD and PDP can not reach. Because of its advantages, in recent years, TV stations have popularly used DLP splicing screens as the background of the studio, and well-known TV stations such as CNN, BBC, SKY, CTV, and other famous TV stations have achieved very good program effects after use.