Videowall processors are available with a wide range of features and capabilities. Many of them relate to system performance, image quality, and reliability, while others can help streamline system design and integration needs targeted at specific vertical market applications. Support for these features will vary by manufacturer and model.
Most of the features and capabilities discussed here are relevant to common videowall system designs. When selecting a videowall processor, it is important to understand more than just which source formats, and how many input and output channels must be supported. Assessing the environment and application for the videowall will help identify the most critical features a videowall processor must support. When comparing between processors, be aware that manufacturer claims of capabilities or performance are often represented by inaccurate or misleading specifications in brochures and on Web pages.
Many videowall processor features relate to system performance, image quality, and reliability, while others can help streamline system design and integration needs targeted at specific vertical market applications.
Centralized videowall processors use a data bus to transport video from their inputs to their outputs. Some systems incorporate a dedicated bus for this purpose, while other systems use a common bus for transferring video as well as other inter-system communication. Use of a dedicated video bus ensures that the transfer of video data is not impeded by other activity, providing more reliable, stutter-free video playback, and ensuring the processor responds to user commands in real-time.
Some end users will want to add more input or output channels over time. This may be part of a phased installation, or an unforeseen upgrade. While some processors are easily expandable, some have a “fixed configuration,” and cannot be changed after leaving the factory. Other videowall processors are upgradeable, but may require on-site support from their manufacturers to make hardware configuration changes. For a distributed videowall processing system, or a centralized videowall processor that accepts sources streamed over a network, potentially up to hundreds of input sources may be supported.
For videowall processors used in missioncritical or 24/7 environments, redundant and hot-swappable components are essential. Redundant, hot-swappable power supplies keep processors running during a failure, and facilitate replacement without powering down the unit. Hot-swappable fans can quickly and easily be replaced if necessary. The ability to replace these components, without removing the videowall processor from the rack will minimize downtime.
Figure 3-6. High quality scaling maintains critical image details when content is downscaled.Hard drives are one of the first points of failure for a PC. Videowall processors with hard drives can become inoperable if failure occurs. To reduce this risk, some videowall processors use RAID or removable solid state storage for their operating systems, rather than a single hard drive. Removable solid state storage virtually eliminates the possibility of hard drive failure, while adding the benefit of reduced boot time.
Maintaining image quality is crucial for videowall processors, which often display large images at high resolution, or downsize images into smaller windows or “thumbnails.” Depending on the quality of the image processing, scaling sources up or down from native resolution can compromise image integrity. Poor scaling can produce artifacts, which can make imagery ineffective for applications requiring critical analysis of images.
Figure 3-6 on the next page shows how visual information is preserved or lost when high or low quality downscaling is applied. Since image quality frequently must be judged subjectively, the best way to assess scaling performance is to see a videowall processor in operation at a site, or in a demonstration where the system is displaying content similar to what will be presented in the intended application.
Figure 3-7. Full color depth processing avoids color banding artifacts associated with a reduction in color resolution.Incoming source signals can vary widely in signal format and resolution. Quick, accurate input detection and configuration of input sources is ideal.
Full color depth processing is required to preserve the quality of 24-bit video or complex graphics without introducing color banding. Some videowall processors reduce the color depth of incoming source signals to reduce bandwidth on its video bus. While this helps preserve realtime performance, color reproduction will be compromised. Figure 3-7 illustrates the color banding artifact. This bit reduction may not be noticeable on simple content such as computer desktops or data screens, but may be noticeable with high-definition video and rendered graphic visualizations.
Incoming source signals can vary widely in signal format and resolution. Quick, accurate input detection and configuration of input sources is ideal. Slow auto-detection can produce blank windows that are presented for an undesirable length of time when switching between window layouts or input sources. Inaccurate input signal detection can result in images shifted horizontally or vertically, displayed at the wrong aspect ratio, or presented with other visual distortions and artifacts. Manual programming to correct these issues for each input can add weeks of programming that could have otherwise been avoided if quick and accurate input detection was supported. This capability also makes integration of new sources, or temporary sources such as guest laptops, simple and easy.
When a videowall processor detects an analog input signal, it typically compares it to a list of known formats, and selects the closest match to determine the signal parameters. Another technique is to examine certain elements of the signal, such as sync polarity and line timing, and perform a source capture based on VESA standard CVT - Coordinated Video Timing or GVT Generalized Timing Formula calculations for the signal parameters.
Complications can arise if there are non-standard signal formats, or if the sources are altered by upstream signal processing or signal extenders. Both situations can prevent accurate detection of incoming signals. To correct this problem, a videowall processor should allow customization of input signal parameters. This will permit manual adjustment of input source sampling to ensure proper source display.
Some processors allow custom source profiles to be created for each input, while others allow the custom profile to be created just once and then shared across inputs, reducing integration time and complexity.
Some videowall processors allow for customizing the resolution of the outputs. This is useful if the system’s display devices are of a non-standard resolution, or when the display device’s resolution is not included in the processor’s default output mode table.
When projectors and projection cubes are stacked next to each other, there is no appreciable image-to-image gap between the displays. However, flat-panel displays typically have a wide physical bezel around the active picture area. The active picture area stops at the inner edge of the bezel. Therefore, when flatpanel displays are stacked together to form a tiled display, there can be significant screen-to-screen gaps across panels.
Determining the number of pixels a mullion occupies is a simple task. Applying this calculation can save time that will otherwise be wasted by guessing or "eyeballing" the adjustment.
The following example calculation is based on a 52 inch (132 cm) 1080p LCD panel with an active viewing area of 45.375 x 25.5 inches (115 x 65 cm). The top and bottom mullions each measure 0.83 inch (21 mm), and the left and right mullions each measure 1 inch (25 mm).
Determine the horizontal pixels per inch - PPI by dividing the number of active horizontal pixels by the width of the active display area:
1920/45.375 in = 44.26 Horizontal PPI
Determine the vertical PPI by dividing the number of active vertical pixels by the height of the active picture area:
1080/25.5 in = 42.35 Vertical PPI
Calculate the necessary mullion compensation for the left mullion by multiplying the width of the left mullion by the horizontal PPI:
Left Mullion Compensation = 1 in x 44.26 PPI = 44.26 pixels
Repeat the calculation for the right mullion:
Right Mullion Compensation = 1 in x 44.26 PPI = 44.26 pixels
Add the two values to arrive at the total horizontal mullion compensation:
Total Horizontal Mullion Compensation = 44.26 + 44.26 = 88.52 or 89 pixels
Calculate the vertical mullion compensation using the same approach:
Top Mullion Compensation = 0.83 in x 42.35 PPI = 35.15 pixels
Bottom Mullion Compensation = 0.83 in x 42.35 PPI = 35.15 pixels
Total Vertical Mullion Compensation = 35.15 + 35.15 = 70.3 or 70 pixels
In the videowall configuration utility, enter a value of 89 pixels for the horizontal mullion compensation, and 70 pixels for the vertical mullion compensation.
Figure 3-8. With mullion compensation, images appear more natural on a videowall.If a video processor does not account for the gap between displays, the result looks unnatural, as objects that span screens appear to “jump” between them. A processor can compensate for this effect by clipping away a small percentage of the image which should physically be positioned behind the bezel. See Figure 3-8 . The sidebar details the calculations to determine the horizontal and vertical mullion pixel sizes necessary for proper mullion compensation.
High-bandwidth Digital Content Protection, or HDCP, is an encryption system widely used for content delivered by Blu-ray Disc players, satellite and cable TV receivers, and PCs. To properly display digital encrypted content, all devices in the signal chain must be HDCP-compliant. The increasing use of digital video sources has made HDCP compliance a growing requirement for videowall processors.
The greater the source placement and windowing capabilities of the processor, the more flexibility there will be to create the window layouts that satisfy application requirements.
Some videowall displays comprise multiple projectors that overlap with each other to create one large, seamless image on a front or rear projection screen. In these systems, imagery must be duplicated between displays in the overlapped region. Also, brightness, contrast, and special color adjustments must be available in zones to balance brightness and color across the blended and unblended regions.
Duplicating the imagery required for edge blending is a feature that may not be available on every processor. Some processors may support zoned brightness and color adjustments, but this capability can also be supported by many projector models. Dedicated video processors are also available that support zoned brightness and color adjustments. Careful evaluation of projector adjustment and videowall processor capabilities are required when designing edgeblended systems.
A videowall processor’s ability to display source windows varies greatly from manufacturer to manufacturer. Some processors allow up to four source windows to be displayed on a single screen, while other processors allow dozens of windows to be presented per screen. The ability to display the same source in multiple windows or multiple outputs at different sizes can be beneficial for very wide videowalls servicing segmented workgroups in a large room. This capability may not appear to be an obvious requirement when first specifying the processor.
The greater the source placement and windowing capabilities of the processor, the more flexibility there will be to create the window layouts that satisfy application requirements.
Some videowall processors can output multiple signal formats simultaneously. This is useful for systems that incorporate displays of various resolutions, such as a videowall comprised of large 1920x1080 projection cubes flanked by 1366x768 flat panels as auxiliary displays. However, processors limited to one output format should feed a signal at the native resolution of the videowall displays. For auxiliary displays, signals from the processor may be upscaled or downscaled to match their native resolutions.
Figure 3-9. Videowall presentations can be enhanced with window borders and titles, as well as clocks.A videowall processor’s ability to add colored borders and text to source windows can be a powerful feature in many applications. Colored borders can denote the status of the content in a command and control room, such as green for unclassified data and orange for top secret data. In a traffic monitoring environment, a red border can help highlight an accident, or colors can be used to indicate traffic levels. Overlay text can be used to provide information about the source, such as the location of a reporter, and the local time. Clocks displaying the time for different regions or time zones can be generated by many processors, allowing an integrator to streamline system designs by avoiding the need for external clocks or status displays. See Figure 3-9.
Some applications may require a touchpanel controller, or use of a customized application for videowall control. In these systems, the videowall processor must support Ethernet or RS-232 remote control. The range of control options will vary from manufacturer to manufacturer, so it is important to make certain that all required control capabilities are supported. This topic is covered in detail in Videowall Processor Control.
Videowalls in data-driven environments such as utilities and network centers often require the ability to manage applications presented on the videowall using a keyboard and mouse. This can be accommodated by installing and operating applications directly on some videowall processors, much like a PC. Other solutions integrate hardware or networked software switching systems to manage keyboard and mouse control directly on the source machines. Software solutions require compliance with operating systems and network security requirements, while hardware solutions require more cabling and control integration.
Visualization or simulation applications may require presentation of 3D content. Few videowall processors currently support this feature, since 3D imaging is a specialty application. Additionally, the system’s source devices and displays must be compatible with 3D content and signals. When discussing requirements for 3D with an end user, be sure to point out that there are two different types of 3D presentations, passive and active. Passive 3D requires polarized glasses for viewing. Active 3D requires electronically shuttered glasses that receive timing information from a transmitted synchronization signal.
Some organizations require that a smaller presentation of the videowall be viewed elsewhere in a facility, on one or two screens, or be streamed to another location. This allows other staff to see an overview of the videowall, without requiring use of a large number of display devices. Some processors provide a preview output of the videowall within the control software, or automatically generate an output that can be connected to a display. Other processors allow preview layouts to be programmed and presented on additional outputs. This method requires that the videowall processor supports presentation of a single input on different displays and different window sizes, a feature not supported by all processors.
All video processors will introduce a degree of throughput latency, resulting in the processed output being slightly delayed when compared to the original input source. The amount of latency will vary from a few milliseconds to several hundred milliseconds, depending on the amount of processing being performed, and how efficiently the processor is executing its tasks.
A delay of a few hundred milliseconds may have a negligible impact on presentation for most videowall applications. However, it can be a concern for installations where the videowall is displaying camera feeds for a live event. A throughput delay greater than 40 to 75 milliseconds will introduce a noticeable loss of synchronization between live or house audio and the camera feeds on the videowall. Delays greater than 100 to 200 milliseconds will be unacceptable for operators using a mouse to work with a computer source presented on the videowall. When calculating throughput latency, one must include any other devices in the signal chain that could introduce delay, such as signal extenders, additional scalers or video processors, and displays.
When designing a system, focus on fulfilling the most critical features needed for the application. Ensure the videowall processor you select will satisfy the application’s requirements.
No single videowall processor offers every feature and capability presented in this guide. When designing a system, focus on fulfilling the most critical features needed for the application. Ensure the videowall processor you select will satisfy the application’s requirements. Where specifications and marketing information are not obvious, insist that the manufacturer’s support staff be able to clearly verify that your requirements will be supported. A videowall processor that was extremely successful on one project may not be the best choice for the next project.
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