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Multi-image displays

I am often struck by the similarity between control rooms of 40 years ago and those of today. Of course there have been changes, but the primary functions haven't changed much. An audio person listens to the mix on speakers, the technical director controls the video on-screen using a switcher, and the director picks shots from an array of monitors in front of him. One thing that has changed is the monitor wall.

Increased flexibility

Modern digital techniques have changed the technology we use in fundamental ways. In an interesting parallel to the sampling in a CCD, monitors are no longer scanned with lines, top left to bottom right. Like a CCD, the image is formed all at once, and the entire screen is refreshed one frame at a time.

Flat-panel displays are like large memories with a light shining from them. If you can treat the surface of a display as memory, it's easy to see how you can write to any part of the memory independently.

Imagine an arbitrarily large monitor, like the 103in monster plasma and LCD displays manufacturers build for bragging rights. That display of more than 30sq-ft could hold a lot of information. (The resolution would be limited to 21 pixels per inch if it was 1920 × 1080). Thirty-five years ago, a monitor wall that large would have sufficed a lot of control rooms. It might have held two dozen monochrome monitors that were likely 8in to 12in diagonal, plus a deluxe 19in program monitor and a clock mounted in racks with spaces for cooling.

Today the flexibility is pretty astounding. The layout is completely fluid and can be adjusted at will, with no space between virtual displays on the plasma canvas. Monitors can be an arbitrary size due to the high-quality resizing engines built into display processors. The layout can be stored and recalled at will, allowing reconfiguration between shows, or perhaps when one of several displays gives up the ghost during a show. Tally lights, always the bane of a design engineer's existence, are built-in and include naming nomenclature to boot.

Generally, display processors, or multi-image displays, are many-channel DVEs. Most can combine the outputs of SD and HD sources, computer outputs and internally stored graphics for backgrounds and virtual monitor edges. Often, internally generated clocks are possible in various formats. Some systems permit monitoring other parameters, such as embedded and discrete audio (levels and phase), closed captioning, V-chip data, teletext, aspect ratio and safe area markers, and even test and measurement data. Such flexibility does not come cheap, in complexity or cost, but it allows monitoring in ways that individual monitors could never replicate. Need a 36in program monitor surrounded by 11 small monitors? Unlike 10 years ago, this is possible today. Tie such a system to a routing system or production switcher, which can pass tally information forward, and the display processor will make the facility appear transparent to operators.

Easy expansion

The physical structure of these systems can allow for expansion to many outputs and support for various inputs. This happens in one of many ways. Some systems have internal routing switchers that permit HD, SD, analog and computer inputs (DVI and VGA) to be switched to any position on the display surface. One company even provides an output from that internal router to connect to external devices, like test and measurement systems or program bypass switching. Some systems have a fixed number of inputs to a single internal matrix, often in groups of 32. Others have methods of connecting multiple systems into much larger virtual systems where the number of inputs can grow to well beyond 100.

In an interesting twist in virtual display routing, at NAB2007, one manufacturer introduced a system that lives inside of an existing router instead of requiring the router to be added to the display. This approach yields less external wiring and vastly expands the number of available inputs, essentially without practical end. Coupled with multiple output capability, systems that have flexible structures can adapt to any useful monitoring application, from large network operations centers, to mobile units, IPTV headends, production control rooms and central equipment rooms where QC functions might be combined.


Output flexibility is particularly important. Two years ago, it was rare to find a flat panel that supported a full 1920 × 1080 image. However, when displays capable of 1080p were introduced to the consumer market, it changed everything. Now it is commonplace to use at least that much display resolution in professional displays.

Following in the footsteps of Apple's 30in Cinema and Gateway's new XHD 3000, both with 2560 × 1600 pixel resolution, it will become more commonplace to up-res HD sources on larger monitors. Master control operators benefit from having a high-resolution display that can credibly show high-resolution virtual monitors in a complex matrix display. New display technologies, like organic LEDs, promise to drive that resolution even higher in the next few years.

Window on the world

An important attribute in multi-image displays is their integration with other devices and control software. Devices that focus heavily on the integration of control applications with monitoring systems result in holistic systems that allow the display and monitoring applications to work closely together. This enhances the workflow, particularly in master control applications. The display environment is suited to the task at hand, and it evolves as operators troubleshoot problems.

As these systems become more complex and technically capable, it will be hard to choose between them. Maximum display resolution and support for advanced features like SMPTE Active Format Descriptor (AFD), metadata display and tie-in to SNMP monitoring systems will enhance the lifetime of multi-image displays. If that 103in display becomes a 4K window on the world, the days of discrete monitors will be numbered.

John Luff is a broadcast technology consultant.

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