LED full color display applications and technical specifications

After SARS, stepping up the formation of many projects the situation. The major manufacturers of LED large screen the contract amount and up 20% over the same period last year, some even almost doubled over last year. There are many new entrants to full-color large screen areas of the company, the results are also excellent. Compare with previous years, this market sprout early, many large projects have been implemented there are million yuan more than a dozen projects. Into the third quarter, a number of major projects into the bidding stage. Another feature is the marked increase in business investment projects, these projects include applications in commercial advertising. It can be said, LED big screen as a commercial advertising medium, after nearly a decade of silence, once again by the advertising industry's favor. At the same time, the whole situation is also encouraging the export of color. In early September, held in Shenzhen, the annual Fair of light, this exhibition is the largest LED industry over the past year show. Large LED screen, LED lighting, LED traffic lights, LED production equipment, testing equipment, dazzling shows that a new upsurge of China's LED industry has come. I believe that this exhibition is a sign, symbol of China's LED industry reached a turning point localization. Internationally renowned manufacturer of LED light tube, screen manufacturers have begun a large scale to the mainland of China, China will become the manufacturing center of LED and its products. Broad market, a good investment environment, low labor costs, making China the world's electronics industry has become the manufacturing center. Just as computers, mobile phones, televisions and other electronic products, China is also large LED screen industry's manufacturing center.

LED large screen in a long-term R & D scientists, the author has been concerned about China's development of the cause of LED large screen, large screen display industry, the international attention the new results. Three years ago, the author of "LED big-screen Development Discussion" article, about a few of LED large screen applications and features, and make full-color large screen in the main image of our projects. It should be said that the overall pattern has not changed, but the increased demand for commercial advertising is also very important trend. We can say that our full-color large screen LED industry is ushering in a new climax. Careful study of market development and technological progress of the new situation, take the right measures, to seize the opportunity to quickly increase and sustainable development, should be peer-worth studying. Here take the liberty to make the technical specifications and other issues, peers and experts hope the correction.

1 image project: aiming at the international class

Image of the project refers to the main purpose of the construction of a large screen is a major city or event to add a style, it does not directly create economic benefits, but the city can raise awareness, shape the city's image, improve the investment environment, create a business climate conducive to economic development, good social benefits, thus indirectly creating economic benefits. Image of the main government investment projects, focusing on social, rather than, or not primarily achieved through cost-effective business operations. In recent years, many parts of the country's urban centers of the construction of a large plaza or public leisure square LED large screen, is a typical image of the project. LED display a large number of sports venues, sports venues is necessary modern facilities, also are in this category.

Is the image of engineering, it is bound to pursue the highest possible perfection of the performance and effectiveness, especially in high-quality video images. In layman's terms is to make a giant color TV, which is many domestic manufacturers have long been trying, but also made considerable progress, but our ideal goal from a long way, full-color with large foreign screen, the gap is still very great.

Earlier this year, Nanjing Hunan Road commercial street, has invested heavily in the construction of an area of ​​114 square meters large full-color screen, the screen built by the British UNITEK company, has been running more than six months, from the point of view, called the current the best domestic large-screen. I participated in the development of screen technology indicators and final acceptance testing, feel there are many aspects worthy of study and emulate domestic counterparts.

As a full-color large screen, the key technical indicators are: a high enough brightness, viewing distance and angle; good color reproduction; high enough gray capacity; scan refresh rate high enough. High enough video signal processing capabilities, in particular, better consistency, structure, process, also have great effort. Hunan Road when a large screen set in the tender specification is:

White balance brightness greater than 5000cd/m2;

White color temperature 6500K;

Video processing precision is greater than 10bit;

Gray level of each color than 10bit,? Can display 1.07 billion colors;

Refresh rate greater than 400Hz;

Display no noticeable chromatic aberration, color difference is less than the full screen of each color 4nm;

Display no noticeable brightness difference between adjacent pixel brightness is less than 5%, indicating the red, green and blue monochrome gray screen, no noticeable mosaic;

MTBF greater than 5000 hours, MTTR less than 30 minutes;

Objectively speaking, these indicators, not only at the time, that is, today, domestic manufacturers of products not yet fully achieved. In many cases, the LED level, the normal design of large-screen brightness is not a problem, can meet the requirements. But the brightness is an important indicator, but not all. It is now widely felt the domestic manufacturers than a large screen brightness, soft enough, the overall effect is less well-known manufacturers, the reason is that there are more technical problems have not been resolved. I believe that from a technical point of view, it is necessary in the following aspects.

(1) color and color mixing

Big screen is composed of a large number of light-emitting diodes, light emitting diodes must be used in the optical parameters of design, calculation and testing in order to achieve a good white balance. Simple estimation and it is impossible to determine with the naked eye feel good effect. Here is to use light-emitting diode and driver design, not only affects the optical properties of the screen, but also affect the reliability. Especially in indoor full color design, thermal design should be taken seriously enough, otherwise the effect and reliability will be a problem.

(2) chromatic aberration correction

Because differences in color coordinates, color television video signal and LED color gamut domain there are differences, resulting in broadcast television color seems unreal. Therefore, the color coordinates of the correction is very important. Correction conversion calculation is more complex, difficult to use software to complete, the products from the manufacturers point of view, even though we all claim to have this color correction, I am afraid not to do color correction.

(3) Consistency

Full-color large screen of the most difficult is consistency, or that the audience most likely to be aware of the problems is that consistency is not good, the screen appears a deep one shallow, commonly known as the mosaic, is the most disgusting. Consistency caused by bad for many reasons, including the use of light-emitting diode, drive circuit, structural design and construction. However, unless the use of discrete light emitting diodes too, but otherwise the consistency of the problem is the design and construction problems. Hunan Road big screen, the audience's first reaction is not observed mosaic (strictly speaking, is not no light, general audience and professionals have observed some differences). This technology on a large screen in the structure is very characteristic, does not use the modules in common use plastic irrigation and other measures worth studying. Typically, the light-emitting diode light-emitting diode according to the manufacturers to the brightness and chromaticity is divided into several files, the difference is the same file through careful design and debug solution. Poor structural design and construction, the phenomenon is caused by mosaic Another reason, often to a large screen installed and put into operation only when found, has been unable to remedy, so it should be particularly hard. If we say that domestic manufacturers display in some gaps on the electrical specifications, then the structure and process in the gap is much larger, these are often seriously affect the display.

(4) gray level

Hunan Road and abroad, many big-screen big screen experience has shown that gray-level must be high enough. The current high-end products is generally the same screen

Display 1024, 10.7 billion colors. Most of the 256 domestic, a far cry. Many manufacturers put 1024/2048/4096 or 16384 coding, 256 non-linear display 16.7 million colors. There is a view, 256 non-linear gray-scale screen should be enough for large, because HDTV standards also provides 256 levels of gray. According to my tests, is not the case, the actual results vary greatly. In fact to achieve 1024 or more gray, will increase the number of technical difficulties. Simple calculation will understand. When the refresh rate of 400Hz, the non-linear gray scale of 1024, to adjust the brightness level of 32, then the correction factor if Ah 2.8, PCM minimum width modulated pulse width is 10ns or so, has reached the drive circuit bandwidth limit. It is impossible to achieve, to consider the complex amplitude and width adjustment approach used. Similarly there are bandwidth issues, ranks as the number of multi-screen, high refresh rate requirements (eg 400Hz and above), the data transmission will increase the difficulty, and sometimes must use optical fiber transmission, in order to ensure image quality. Therefore, non-linear gray scale from 256 to the non-linear 1024, requires a leap in technology.

(5) digital processing capabilities

To get high-quality images, you must have high-quality video sources. For the average large-screen users can get the best signal is the broadcast TV signal, DVD, VCD and so only household level. Therefore, the input signal digital processing to enhance image quality is indispensable. In fact we have such an experience: Play through the selected program, the display is very satisfactory, but if it is screened live TV or VCD / DVD, it is inevitable that a variety of screen and lens, such as night scene or dark screen large area of ​​high-brightness bright screen, then the effect is being reduced. How can a variety of screen and lens are satisfied with the results? It is up to digital signal processing, such as digital comb filter, noise filtering, edge sharpening, remote prediction and compensation, color correction, non-linear fixes and so on. It is particularly worth mentioning is the scaling (SCALE) treatment, is the special problems of LED large screen, up to the big screen industry efforts to study. As the big-screen pixel is always less than the video information source, playback will face scaling problems, sampling and reproduce in the loss and defects caused by aliasing and image quality will result in decline. How to reduce losses and reduce the need to digital signal processing technology. Digital image processing technology has made great progress, there are many results, such as large TV or projection in the technological achievements can be directly applied to large-screen display to. Digital processing system embodied in the processing capacity and processing speed on the median, the use of high-end DSP or FPGA is an inevitable trend.

(6) reliability and life

Reliability is the display of life, whether it is for the image project, or for commercial operation, reliability is essential. Reliability index from the mean time between failure (MTBF) and mean time to repair (MTTR) to express. MTBF10000 hours is a very high target, in fact, does not necessarily need. Many manufacturers are a big effort to improve system reliability, but how to achieve what level, and can not provide convincing data. Currently, there are no big-screen conducted for reliability testing. Reliability is based on rigorous reliability design and strict quality control. Display is a large electronic equipment, to ensure good maintenance and regular maintenance conditions, the indicator can reduce the MTBF, cost savings. The reason is simple, if you do not require large-screen long-term continuous operation, but intermittent work, and in the interim period, through the maintenance, to eliminate signs of failure, the system is always in good condition, then, can not guarantee the normal work period failure. So, 1000 hours MTBF also make the system stable and reliable operation. Hunan Road big screen, from the opening, it has been running for eight months, no significant decline in key indicators. This is not only because of the higher system reliability, but also because of maintenance done well. More prominent is the large screen with good design and spare parts, MTTR can reach 15 minutes, which is especially worthy of us to imitate.

2? Commercials: try the best price-performance

The most striking and encouraging is that for commercial advertising, full-color large screen is on the rise a new boom, which is both the requirements of economic development is the result of technological progress. I believe that in the face of this tide, take the right business strategy and technology strategy is to ensure sustainable development. First of all, users and audiences respond to the necessary guidance to ensure sustainable development and a higher level.

From a technical point of view, I believe, is not the pursuit of the best picture, but the pursuit of the best cost performance. To text, animation and screen based on processed images, do not focus on video, does not even require live television.

The emphasis is on business operations cost, as an advertising media to attract the audience's attention, advertisers get the recognition. In short, must be large-screen manufacturers, advertising operators and advertisers have benefited. In a variety of advertising media, the big screen is that it changes fast, colorful; disadvantage is that large investment, high cost and expensive. How to reduce costs, reduce cost, there are many good ways in recent years, technical indicators here would like to make some views.

(1) Function: The purpose of advertising is to promote, attract attention, to establish a deep impression on the audience, beautiful picture is important, but it is not only a video or television program is the best. Through a variety of ideas, changes and other means can also achieve good results. Neon changes very limited and so few come and go pattern, the effect is not bad. Big-screen manifestation of more than neon, enough advertising purposes. That there must be full-color video effects, to the idea of ​​big-screen performance is one-sided. In fact, in the United States, not many big-screen video, concentrated in certain areas, such as New York's Times Square, Las Vegas Las Vegas, etc. In order to avoid the attention of drivers dispersed, fast-changing U.S. law does not allow advertising. Changes in text and simple graphics should be more sales with advertising. Animation (such as FIASH) may be the best performance of the method. In China, it is customary to screen a large screen is divided into synchronous and asynchronous screen categories. Like a computer monitor screen simultaneously, changing, full-featured, but the efficiency is low, the work requires a computer and communication is always running. Screen is asynchronous microcontroller or embedded system control and display the contents of the write-once, until the next update so far. Gray high-end processor and video to achieve the same effect, asynchronous screen in many cases more suitable for advertising and information on slowly changing, but not for the general user acceptance.

Simple microcontroller or small embedded system processing capacity, and the display of grayscale and refresh speed will be lower. However, in the performance of text, animation and screen a variety of change, still have enough capacity.

(2) brightness: As we all know, direct sunlight in outdoor conditions, the need 5000nit brightness in the room 1000nit around enough, and half outdoors between the middle of these is the consensus of the industry. Can imagine, a large outdoor screen if only work at night, light indicators can greatly decrease the cost of course decline. This means that if the big screen, do not work during the day, evening shows, as a commercial advertising should be a good idea. In fact, the neon is currently the most widely used outdoor advertising media. Neon brightness is much higher than the large LED screen, but it does not require the neon open during the day, then why the big screen during the day and work demands? But also in direct sunlight it broadcast video program clearly visible, in fact, there is here to guide users. Moreover, during the day and at night the audience much more than that, is it more effective. Taiwan. Company launched a billboard, the screen is fixed during the day, evening activities are full-color screen, the cost is only common outdoor full color one-third, is a smart approach.

(3) Resolution: depends on the resolution, said resolution or pixel density, the cost of the display, the pixels of the cost accounted for more than half. Therefore, to reduce the cost of pixels is the most attractive, dynamic pixel pixel splitting technology or technique is commonly used methods. Dynamic pixel technology is not new technology, have spent more than a decade at least, it is shared by the composition of the pixel approach to improve visual resolution several times. For example, the most commonly used 2R1G1B sharing allows separation d of the large-screen visual resolution to d / 4 effect, the result is fewer pixels can display a larger picture. It must be noted that the visual resolution of d / 4 of the dynamic pixel screen is not the same d / 4 the physical resolution of the big screen, many domestic manufacturers in promoting dynamic pixel technology, sometimes exaggerated. Dynamic pixel technology to achieve many different ways, are the use of residues as the principle is the use of the human eye's persistence of vision, with fewer pixels can display the activities of the larger picture. But it must be pointed out that the dynamic pixel technology, with fewer pixels large display screen due to aliasing effects will blur the image, clarity is poor, sometimes blinking, and not as good as the real pixels.

Last year, Shibuya, Tokyo, Japan, a large commercial buildings, built a size six-story electronic display. The screen mounted on the inside of the glass curtain wall, does not affect the building's appearance and lighting. Play video ads at night, through the display unit of space, you can see the lights inside the building. As to avoid the harsh conditions of outdoor work, the cost is greatly reduced. The widely spaced points, using the residual as the technology, the number of pixels is only a quarter of real pixels. ? Effect though not compared with the full dot-matrix screen, but the Nasdaq in New York than the big screen, saving money and new ideas, it is worth promoting in areas where conditions permit.

It is worth mentioning that Shenzhen Tian Hui's blending full-color, not by reducing the pixel method, but rather to reduce the high price of pure green, pure blue tube means, and through clever structural arrangements, access to a very good blending effect, its cost performance is conducive to the popularity of full-color applications. This method is based on the theory of the human eye for the brightness of the power of high-resolution, low resolution for color, color TV is using this principle to reduce the bandwidth. However, we all know, in the three primary colors to white, the green of the largest contribution, thus reducing the green tube, is bound to affect the brightness of the screen, so this method does not require high brightness applications.

(4) Reliability and life: on the reliability, as already discussed, here to talk about life issues. Life is not restored to the system to the technical specifications of the time, with reliability, but not the same concept. Life depends on a large screen LED life. LED life is the LED light intensity dropped to half the nominal value of the time. Long-life LED, as electronic devices in military supplies, the price is much higher. LED tube light attenuation and the quality of the work of a great bearing on current and working environment, even brand-name long-life tube, if the state does not work properly, life will be shortened, which are related to costs. Almost all manufacturers have LED's life as a big-screen life, in fact, is wrong. Big-screen life is what should be many, but also a problem of cost performance. Computing business operations and return on investment screen, there is an o