Multi-image displays

Television facilities have been quick to adopt multi-image display processors for monitoring multiple feeds of video, audio and associated metadata. The initial driver was the development of large multichannel playout facilities, which demanded a larger scale of monitoring, with more flexibility for changes in channel counts. These installations also required a higher degree of efficiency and cost-effectiveness, with fewer operators per channel.

Multi-image display technology is now used widely in mainstream broadcasting. It has been especially beneficial for centralized broadcast operations, which have involved the co-location of monitoring for multiple small stations into fewer, larger facilities. These facilities have benefited from fewer staff managing more channels, without sacrificing the great level of control needed to maintain high-quality broadcasts.

Multi-image processors in master control

In master control environments, signals need to be monitored throughout the transmission process to ensure they are delivered properly, and that video, audio and metadata are valid. The monitor wall needs to incorporate not only outgoing feeds, but also incoming return signals, which must emulate programming as it would appear to viewers in their homes.

A high-performance, multi-image master control processor will provide a wide range of signal monitoring capabilities, including loss of signal, freeze, black and excessive luma. The audio will also be monitored, with detection of presence, silence, overload, out of phase, Dolby metadata and mono signals. Metadata detection will often include presence and display of closed captioning and subtitles, Extended Data Services (XDS) for VBI data used with analog NTSC systems, widescreen signaling (WWS), aspect format descriptor (AFD), source ID (SID), Dolby Digital dialnorm and channel line-up. For effective operation, the multi-image processor must be capable of monitoring all this data simultaneously. It must also report validity status intelligibly to the operator with on-screen status indicators or by displaying the relevant signal data. It should report any signal anomalies to a log manager for future investigation.

The most sophisticated display processors also offer close interfacing with facility management systems, allowing an operator to take a comprehensive and in-depth look at each signal as it passes through a facility. Some processors can also interface with the station's automation system to collect and display pertinent program information, such as the name of the clip and its duration. By displaying this data near the video window on the monitor wall, the processor helps the operator anticipate events and ultimately better manage the playout process.

Monitoring HD programming brings up new video quality challenges, as well as aspect ratio issues. Differing aspect ratios are much easier to accommodate with a monitor wall than with traditional CRT monitors because 4:3 and 16:9 material can be handled with equal ease. In many cases, the monitor wall and display window will adjust automatically to suit the format of the incoming signals. Along with HD comes the use of 5.1 audio and its six audio channels. Operators must be able to use the monitor wall system to observe multichannel audio data levels and ensure that all the audio channels are properly aligned and compression levels are set appropriately.

Multi-image display in production environments

In some ways, the production environment is more demanding on multi-image processors than master control. This is because the processor must be able to display video with the absolute minimum of delay, with high accuracy and without processing artifacts. The value of multi-image display processors for production is not limited to the studio. Their versatility in accepting and displaying feeds, coupled with relatively low heat generation and low-profile design, makes them ideal for mobile production trucks.

During typical production tasks, operators need to have access to many feeds, displayed in virtually any configuration, and complemented by tallies, text labels, source names, clocks and timers, as well as source format and aspect ratio safe areas.

Some multi-image display processors provide interfacing with production switchers, which allows signals selected to the on-air and preview buses to be tallied on the monitoring display. In addition, source labels configured in the switcher can be displayed under each window on the monitoring display. Switcher operators can also change the layout of a monitoring display directly from the switcher to suit different productions or operators. A highly integrated production monitoring environment like this can bring significant improvements in workflow.

Selecting a multiimage processor

The selection of a suitable multi-image display processor and appropriate display can be a challenge. In any application, the reliability of the multi-image display processor is of fundamental importance, as the monitor wall must be capable of displaying images 24/7, with the ability to repair any failure rapidly. A high-quality multi-image display system will provide a temporary monitoring mode that allows the user to supervise all signals using part of the system, while another part of the processor, or display, is repaired. Here, the use of smaller failure blocks, which translates to fewer images per process, can be advantageous in maintaining uninterrupted monitoring, depending on the system topology.

The key reason for buying a multi-image display processor is usually the flexibility it affords operators when monitoring. To make the most of this, the monitor wall must have a powerful yet highly intuitive operator interface. With an efficient interface, operators can quickly call up preset layouts as required for the time of day or specific monitoring task. They can also bring windows to full screen for closer scrutiny or check the status of audio on a particular channel. Some systems also offer a dedicated remote control panel or direct mouse interface, which can be used to select windows or sources faster and with more precision.

Some broadcasters prefer using a smaller processor with fewer inputs to minimize cost and maximize resolution per display. In fact, the history of multi-image display processors began with simple quad splitters designed to save money and space. At the outset, these systems were aimed at entertainment, with multiple events shown on a single display. This technology has now been applied to broadcast confidence monitoring. Added information, such as UMDs, audio level meters and clocks, give users the tools they need to reliably monitor their video and audio signals.

Increase your flexibility

Things have significantly changed since the initial multi-image viewers were launched. Systems available today can combine the multi-image processor with a router in a single, expandable chassis. The router can switch outputs to the monitor as well as feed test equipment and master control or production switchers.

Ultimately, all this new technology is increasing flexibility and functionality, and contributing to more effective workflows. However, it's important to realize there is more than just hardware and software behind the selection of the optimum multi-image display processor. It is essential to pick a company that understands your monitoring requirements and can deliver effective service to maintain the products long after the initial install.

Louis Caron is the multi-image product development manager for Miranda Technologies.