Video wall
A video wall - or also LED wall , video wall , LED wall - is a large display area for displaying moving images .
description
Video walls are often used at major events such as concerts or sporting events. They are now standard in modern stadiums and large multifunctional arenas. Either a camera image or graphic information is displayed on the wall in order to present the viewers with a fan TV, advertisements or statistical data on the events. In contrast to film projectors, electronic signals are fed in . Originally a video wall consisted only of a projection screen or a screen onto which an image was projected by an eidophore . Often several CRT monitors were put together to form a large area, which, however, resulted in an annoying black grid from the spaces in between. Later were Beamer used for projection, the quality of low-light devices, however, much to be desired left.
There are also large screens for indoor applications such as in control rooms for control rooms or traffic control centers. Because of the greater resolution required for this at a smaller viewing distance, however, panels made up of discrete LEDs are not used, but combinations of several plasma or LCD screens with a significantly higher resolution. However, LCD solutions have the disadvantage that there are gaps between the individual screens at the joints of around 6 mm in width. This corresponds to twice the frame width of the individual screens. Electronics ensure that either individual images are displayed on the various screens or an overall image is generated across all screens.
Current, large-area video walls are usually so-called LED walls, which means that they form the picture from many red, green and blue LEDs , i.e. light-emitting diodes that are controlled by control electronics.
The following technical properties belong to the function of a video wall or the description of its technical properties. The image result arises from a complex interplay of these and other factors; Depending on the intended use, the priority can be stored differently. The requirements for indoor use are different from those for outdoor use - among other things, the viewing distance is shorter at indoor events, so a finer resolution is an advantage. When exposed to sunlight in the outdoor area, in addition to suitability for all weather conditions, the focus is on brightness and contrast behavior.
Video walls are also increasingly being used in advertising. In 2010 the largest test market in Germany was created in Saarbrücken with a total of 8 video walls with a size of 9 to 15 m² on federal highways and on busy inner-city streets. The test market has a total area of 84 m² video wall modules (as of June 2011). The motifs usually change every 6 seconds. The network is supplied via a client-server solution with an Internet connection to each video wall. The video walls can be adapted to the content every second, but can also be monitored by remote maintenance. In May 2011, an episode of the crime series Tatort was shot with the inclusion of the video walls in Saarbrücken.
The miniaturization of the LEDs now makes pixel spacings <1 mm possible. New LED packaging (so-called mini-LEDs) combine 4 complete RGB pixels, i.e. 12 individual LEDs, in a single housing with a pre-wired matrix. Such NPP displays (narrow pixel pitch) are mainly used in TV studios but also for conference rooms or digital cinemas. The devices can usually display HDR content in HDR10 / HLG . The next level of miniaturization is represented by micro-LEDs. With so-called COB technology (chip on board), the silicon chips are fitted directly onto the circuit board, where they are wired and encapsulated. At the moment it is problematic to minimize manufacturing defects.
LEDs
Compared to incandescent lamps, light-emitting diodes are characterized by a low power consumption , a long service life and very well-suited and controllable radiation characteristics for image display . Maximum optical quality of a video wall cannot be achieved without the highest quality for this component. Identical properties of all diodes used are also important for a homogeneous image. In the long term, there is always an aging process that is noticeable, among other things, in decreasing brightness and color changes. Modern display controls meanwhile enable "calibration" on a pixel basis. This means that the individual pixels are corrected with regard to their brightness and color.
SMD
While conventional diodes are individually plugged onto the circuit board with wires, SMD LEDs ( surface-mounted device ) combine three diodes, soldered by surface mounting, in a housing on a circuit board . The smaller pixel spacing made possible by the SMD design and the high image quality pay off where the viewing distance is small, i.e. primarily with indoor devices. Thanks to the rapid development in terms of brightness and durability, SMDs are also increasingly being used outdoors.
IMD and mini LED
IMD LEDs represent the next step in miniaturization. Here, 4 pixels, i.e. 12 LEDs, are packed in a single housing and pre-wired as a matrix. With these components, also known as mini-LEDs, pixel pitches of 0.9 mm and less can be achieved.
Technical terms
pixel
The smallest unit for defining an image point is the pixel . Three LEDs in the basic colors red, green and blue each form a unit, a pixel. The more pixels there are, the higher the resulting image resolution of the video wall.
Virtual pixels
With virtual pixels, comparatively fine image reproduction can be achieved with large pixel spacing: The software control calculates the image on the basis of four diodes per pixel instead of three - with an additional red one. In this way, additional - virtual, not physically existing - pixels are created as the intersection between neighboring pixels.
Pixel pitch
The physical resolution of video walls results from the pixel spacing, i.e. the distance from center to center of the neighboring diodes. The values are currently within a range of around 0.9 mm to 25 mm, with a smaller distance producing the finer, higher-resolution image.
Viewing distance
The perception of the pixel distance is put into perspective with the distance between the viewer and the image. As a rule of thumb, the pixel pitch, not in millimeters but in meters, also corresponds to the minimum viewing distance from which the eye can no longer identify a single pixel. 20 mm pixel pitch means a minimum viewing distance of around 20 m. The ideal viewing distance, on the other hand, is 3 times the minimum viewing distance. From here on, a colored area is perceived as completely homogeneous.
Viewing angle
For video walls in stadiums, the viewing angle is between 120 ° and 160 °. The image is no longer displayed optimally for viewers outside this viewing angle.
Color depth
With color depth , the bandwidth is specified in the individual pixel brightness levels of the primary colors of the RGB color space can reproduce red, green and blue. 8 bits denote 256 gradations per color, i.e. a total of 16.8 million possible colors per pixel. The limit of the color depth that the human brain can actually perceive is 6 to 8 bits. The significantly greater color depth in electronic imaging and reproduction is applied (currently 18 bits), serves the purpose of the image contrast dynamic adjust to the ambient light.
Image build rate
The brightness of the individual LEDs in video walls is controlled by the PWM process. A processor controls the switching on and off of the individual diodes with a sequence of very short constant current pulses , in the range of nanoseconds , so that the eye does not perceive this as a "pulsation" of the LED, but as a change in brightness. The image build-up rate is given in units of Hertz or Megahertz (Hz / MHz). This describes how often a complete picture is output one after the other (per second) and is therefore many times higher than the video frequency of the signal source.
Scan rate
Scanning became necessary due to the limited space for the driver modules with increasingly smaller pixel spacing. From a technical point of view, it is a matter of controlling several LEDs with the same driver output. This is implemented by time division multiplexing and is usually done line by line. On the one hand, scanning reduces the maximum brightness by the scanning rate, and on the other hand, a higher image build-up rate (> 2 kHz) is required so that the image does not show any "backlash" on camera recordings.
Brightness / brilliance
The luminance or brightness of an LED system is specified in the unit nit . In the outdoor area, a good 5,000 nits are common, with up to 9,000 nits currently being achieved. In Europe, cd / m² (candela per square meter) is increasingly common instead of the unit nit.
Manufacturing
The majority of all diodes and circuit boards are manufactured in China, Japan, Korea and the USA. German and European providers of video walls also import these components and, in some cases, the entire video wall.
Assembly
Video walls are assembled from modules and mounted in a housing. In addition to the LED circuit boards, the individual elements contain components such as fans that reduce the heat generated during operation. The design influences the suitability of the system under extreme climatic conditions, the ease of maintenance and the service life of the LEDs. A special problem arises when trying to contain electromagnetic radiation and keep it within the prescribed limit values.
When installing in stadiums or arenas, the assistance of a structural engineer is required, and fastening in places of assembly is subject to particularly strict safety regulations.
Mobile solutions
In addition to the permanently installed video walls, transportable devices are offered, especially in the rental business, which can be attached to a crane or truss, for example. In addition, specialized manufacturers offer video walls that are integrated in show trucks with a stage and media technology. The most compact are video trailers, i.e. car or truck trailers including a video wall. Thanks to a generator , such systems are usually autonomous in terms of power supply for daily use .
Legal requirements
An LED video wall generates electromagnetic fields and is therefore also a transmitter, so that radio traffic can be impaired in its vicinity. Video walls and LED boards as electrical products are subject to the supervision of the Federal Network Agency (BNetzA). This explains in one of its leaflets (Federal Law Gazette 2008 Part I No. 6, issued in Bonn on February 29, 2008): “The Federal Network Agency is responsible for the execution and implementation of the law on the electromagnetic compatibility of equipment ( EMVG ) and the Law on radio systems and telecommunications transmission equipment ( FTEG ). According to Section 14 of the EMVG, it is authorized to randomly check devices that are or are being placed on the market for compliance with the requirements of Section 4 and Sections 7 to 9 of the EMVG. This also applies to the requirements of the FTEG. ”Furthermore, video walls usually represent structural objects in the sense of the building regulations of the respective federal states and are therefore subject to both a permit requirement and restrictions resulting from the most varied of local statutes. So is z. B. in the city of Munich, any movable illuminated advertising and thus the use of video walls is not approved. The provisions of the Road Traffic Regulations, here in particular Section 33 “Traffic Disruption”, as well as the emission protection laws of the individual federal states should be observed in the run-up to the planning of stationary video walls.
See also
Web link
Individual evidence
- ↑ Description of LCD large screen solutions from the German manufacturer Jungmann Systemtechnik GmbH
- ↑ a b LED quality. Retrieved February 4, 2020 .