High-Power Projectors Illuminate Opening Ceremonies at 2008 Beijing Summer Games

In August of 2008, the world took in an amazing spectacle as the opening ceremonies of the summer Olympic Games unfolded. Display technology, including projectors, played a major role in enabling this event.

by Terry Schmidt

THE ambitious and spectacular opening ceremonies of the 2008 Summer Olympics in Beijing, China, involved thousands of performers and special effects. The event, designed to dazzle both the 91,000 attendees and a live TV audience of approximately 800 million viewers, was enhanced with a non-stop panorama of digitally projected images on all suitable surfaces inside the 2,777,089 ft.² (258,000 m^2 a) "Bird's Nest" stadium. For these live ceremonies, advance planning, technical competence, comprehensive testing, and system reliability were paramount.

Projectors helped make all this possible, and the ones used in the opening ceremonies were made and installed by Christie Digital Systems of Canada. Although the project began with discussions in 2007, this part of the story begins in April 2008, some 5 months before the games, when a team of managers, engineers, and technologists from Christie had begun working feverishly to organize what was going to be the world's most ambitious outdoor digital video display to date.

Project Outline

The overall display concept for the opening ceremonies involved the blending of multiple high-power digital video projectors on "parapets" or cantilevered plywood platforms from two separate balcony levels with "flown" projectors hoisted high into the roof structure of the stadium. The idea was that the highest elevated projectors would beam images anywhere to the stadium floor. The Tier 2, or lowest balcony units, would beam images to the floor as required on people-powered moving screens. The upper balcony, or Tier 3, projectors would cross-fire images to the vertical oval lip of the roof structure called the "Raceway" (Fig. 1).

This coverage would provide maximum flexibility and an impressively large image surface viewable from many angles. From a technical standpoint, the elaborate set-up was challenging because of varying screen surfaces, reflectivity, angles, distances, luminance requirements, and the sheer size of the stadium.

This coverage would provide maximum flexibility and an impressively large image surface viewable from many angles. From a technical standpoint, the elaborate set-up was challenging because of varying screen surfaces, reflectivity, angles, distances, luminance requirements, and the sheer size of the stadium.

The Projection Equipment

Because the stadium was open-roofed, the requirements for projectors on Tier 3, the upper balcony, included the ability to be safely rigged to high structures, and to withstand exposure to severe outdoor elements. These requirements were satisfied by the Christie Roadster S+20K, which is designed specifically for rental/staging. The projector's 20,000-lm image is powered by a Ushio 3-kW xenon arc lamp and displays 1400 x 1050 pixels from its DLP light engine. Various long-throw lenses are motorized to provide remote controllable zoom, focus, and horizontal/vertical offsets.

The challenge on Tier 3 was to cross-fire to a stationary screen composed of a white stretch of fabric covering the tall vertical surface of the inner oval roof ring. Due to the brightness requirement of this massive surface area, which measured approximately 1900 ft. wide by 50 ft. high, earlier testing demonstrated that it was best to overlay three images from three side-by-side projectors on each of the 21 overlapped screens across the stadium and up to the oval raceway. The unit used for this application was the Christie CP2000-ZX digital-cinema projector, which is powered by a 3-kW xenon arc lamp by Ushio. Each of these projectors provided 20,000 lm from a 2048 x 1080-pixel resolution digital-cinema DLP chip (Fig. 2).

During a visit in April, the Kitchener Digital Cinema team from Christie had to determine if there were any special technical or environmental issues regarding the use of the digital-cinema equipment in Beijing. After inspecting the stadium and referring to local weather statistics, the team concluded that the environmental risks would be low. There was a 0.4% chance that the temperature in Beijing at 8:00 pm on August 8, 2008 – the night of the opening ceremonies – would be over 35°C which was the specified maximum ambient operating temperature for the projectors. The humidity in Beijing during the month of August averages a modest 77%. The chance that water would come into contact with the projectors was only an issue for those units situated in the lower part of the stadium, where strong winds and rain could disrupt operations. Dust was a problem, as the stadium was still a beehive of hard-hat construction activity in April, though that activity was scheduled to settle down by June. Dust and rain covers were made for all exposed projectors when they were not in use.

The Deployed Systems

Between mid-April and mid-June, the technical staff from Christie's offices in Beijing and Shanghai along with its Chinese customer, Wincomn, installed the 84 Roadster S+20K projectors. The projectors were divided into two groups: 33 (including three "hot spares") were "flown" high above the stadium with chain hoists on virtually inaccessible trusses, while 51 projectors were placed on the Tier 2 platforms. A dual-mirror head from High End Systems allowed a computer to aim the bright images over a very wide range of angles. The source material was supplied via fiber-optic DVI cable systems from Chinese supplier Cuanbo. The signal sources were 81 Axon Media servers, also from High End Systems, that had the ability to warp and resize on-the-fly and aim and project images in any orientation, any size, almost anywhere in the Bird's Nest stadium.

  (a)      (b)

The upper ring, Tier 3, was the location of 63 CP2000-ZX digital-cinema projectors that were organized to light up 21 screens on the upper vertical oval opening in the stadium, where each 75-ft.-wide image was warped, overlapped, and edge-blended by an additional 21 Axon servers. At over 1900 ft. long, this generated the world's largest continuous oval image that became part of the spectacular stadium show (Fig. 3).

Pixel-by-Pixel Overlay onto the Overhead Raceway

The overlay of one or more images for increased brightness is not a new concept. In rental/staging venues, it is often done for redundancy. Accuracy of optical alignment is important in high-resolution applications because double or triple ghost images from each misaligned projector can detract from the image quality. The main goal of careful aiming and lens offset is to eliminate keystone distortion (i.e., skewed imagery).

In the Bird's Nest stadium, the precise aim of the projector depended on the adjustment of the front feet and lens mount, all of which were accessible only by having someone climb out onto the platform and manually adjust it. The staff had to master this feat by trial-and-error alignment, so that when someone's body weight was not on the platform, the system remained perfectly aligned; i.e., the setting made while a staffer was on the platform would change as soon as he got off it, and the staffers had to learn to estimate the difference and adjust accordingly. The large throw distances of 400 to over 700 ft. made the aiming errors due to weight change even more dramatic.

In order to aid accuracy, special "red only" and "green only" alignment test patterns were loaded in Beijing on each of the 63 Tier 3 projectors. The center projector of the three was set to red, and each of the outer two to green. Then careful aim and lens-mount alignment was done two at a time, just like color convergence, on green to red.

The attribute of the lens design that enables an almost perfect pixel-for-pixel overlay is called "lens offset." The design of the lens is a telecentric reverse telephoto designed for a larger-than-normal image size. The precision lens mount is adjustable in both X and Y planes without changing the aim of the lens. This design prevents keystone geometry distortion of the image and rectangular images can project onto the screen and overlay accurately. The long throw distances in the Beijing project minimized matching issues caused by curvature and oblique angles to the screen surface.

Technology in Action

The following technology issues all figured prominently in the Bird's Nest stadium project:

Edge Blending: This technique is often used in multiple-projector large-scale productions. However, edge-blending had never been applied before to a project as large as the 2008 Being Summer Games' opening ceremonies. The geometry of the raceway was oval and as one continuous screen could be broken down into 21 sub-screens, each was illuminated by three digital-cinema projectors from the opposite side of the Tier 3 level.

Edge-blending is accomplished by overlapping each screen by about 20% with its adjacent neighbor. This results in a double brightness bar at the overlap if left uncorrected. Correcting the brightness level involves adjusting the contrast drive level down from 100%, just where the overlap begins, to 0% in opposing directions to make the overlap region virtually disappear. Of course, the video content of the two projectors must also be adjusted to "flow" properly from one screen to the next and avoid incongruence for moving content that stretches over several different projectors (Fig. 4).

Fig. 3: The upper ring projectors were outfitted with customized heat extractors (shown at top of projectors) to help maintain viewable site lines.

Image Warping: This is a generic video-projection term that refers to restoring an image to corrected geometry for correct viewing, even though a projector may have an oblique angle to a screen. The latter causes image distortion due to projection onto a curved surface. At the Bird's Nest stadium, the corrections for both this and the edge-blending overlap had to be executed with precision. This proved to be a challenge because of the unique oval screen surface of the raceway and its elevated location; almost 100 ft. higher than the projectors, most of which were at an off-angle to the screen.

Heat Extraction: One of the differences in a projector designed for digital-cinema applications vs. rental/staging is the standard 8-in.-diameter heat extractor. Located on the top of a cinema projector, it takes advantage of a theater's built-in roof extractor system. These extractors are normally designed to take away more than 600 CFM of unwanted waste heat generated by long-life theatrical xenon arc lamps. For the purposes of the Olympic project, which had no built-in roof extractor system, a small, self-contained inline heat extractor was sourced for each projector on the top Tier 3 location. However, in the stadium, this vent location caused noise and interfered with the first-row guests' sight lines.

After the team installed and tested the heat extractors, Director of Lighting Sha Xiaolan decided that the sound was objectionable, especially in the plush seats of the VIP area. The team settled on a sound-attenuating insulated air-conditioning flex duct to relocate the heat extractor off to the side and out of the first row guests' sight lines. The sheet metal of the heat extractor was also sound damped by 1-in.-thick acoustical foam wrap to reduce sound levels by approximately 6 dB.

Signal Distribution: All video signals for the projection systems were produced by 110 Axon servers supplied by High End Systems. These signals were provided as standard HDTV 1920 x 1080-pixel format on DVI connectors. Because some cable runs were up to 1000 ft. long, each DVI signal was converted at the server to four-channel fiber and converted back at each group of three projectors to DVI again. At this point, it was up-converted to the 2048 x 1080 digital-cinema standard for maximum brightness efficiency of the DLP chip. A DVI splitter was then used to divide the signal to the three projectors.

Networking: All 147 projectors were connected to the control room via two separate Ethernet networks. Each was a complex configuration of copper and fiber that handled logistics. These network connections proved invaluable for a range of reasons; from safe sequencing of powering-up approximately 0.5 MW of projection equipment at 5-sec intervals, to remote status monitoring of various functions and remote diagnostics during installation, testing, and rehearsals. The physical logistics of manually checking a projector on the other side of the stadium was a time- and energy-consuming event to be done as infrequently as possible. It took a long time to traverse the stadium at the Tier 3 level, not counting troubleshooting time.

Unexpected Challenges

During June, the team worked from about 5:00 pm to 5:00 am each night to take advantage of the darkness for rehearsals on the outdoor screen (the stadium roof lip). The necessity of security passes and sophisticated explosives screening made for interesting logistics. For example, no Internet connectivity at the stadium was permitted due to concern about terrorist acts. Conveniently, a Blackberry allowed connectivity many times when it was necessary to communicate with Christie back in Canada.

Another challenge was the weather. From a statistical standpoint, the environmental issues discussed earlier were considered to be manageable. However, while the team was setting up for rehearsals in June, a severe thunderstorm occurred. The overhang and dust/rain covers on the projectors did their job, but there were also roof leaks from the fabric covering the stadium, which resulted in large amounts of water dumping just several feet from some of the projectors. Fortunately, none were harmed.

In addition, it turned out that the month of August was unusually hot, even for Beijing. When the projectors were turned on at 5:00 pm on the day of the show, the temperature was a reported 38°C – 3° over the maximum operating temperature of the units. By show time at 8:00 pm, the temperature had dropped to 34.5°C, but the team was still relieved that it did not need to have the heat extractors turned down to reduce noise because it had already solved the acoustic problem with the insulated ducts.

Fig. 4: Edge-blending (taking place in the image blend zone above) was accomplished by overlapping each screen by about 20% with its adjacent neighbor. Warping (restoring imagery to corrected geometry for proper viewing) was especially difficult on the high oval screen of the raceway. Lens offset adjustments took place on Tier 3.

There were of course several challenges of logistics in this very large venue. Safety was always top of mind. All of the projectors were mounted high above seating where a fall of either a person or equipment would have dire consequences. All loose equipment was secured with aircraft cables tied to steel rails embedded in concrete. When adjusting a unit, everyone wore safety harnesses. The team communicated via two-way radio sets, but as mentioned above, it still took almost 20 minutes to walk from one side of the Tier 3 level to the other. Multiple and unknown vendors for support equipment such as network switches and fiber-cable runs added more challenges to the task at hand.

Another challenge the team encountered during the project involved a mysterious set-up change to its resizing equipment. As the team members would come in to power up all the equipment to work for the night, they would notice that some screen sizes had changed electronically and were no longer perfectly matched to their neighboring screens. They also noticed that the IR remote control for the Cine-IPM2K resizing box feeding all three projectors for each of the 21 "raceway" images did not work well unless it was extremely close to the sensor. These seemingly random changes began occurring more frequently. One night, as the team members were adjusting the last of three units in a row that had changed size from the previous day, another one changed in front of their eyes. It finally occurred to someone that the high-frequency metal-halide lighting that was being used in increasing amounts in rehearsals each day was producing enough noise to be picked up by the IR sensor on the CineIPM 2K, resulting in the unwanted changes. It nowbecame clear that the lighting was also inter-fering with the range of the remote control. The team covered the IR sensor with double layers of gaffer's tape and the problem disappeared.

One of the serious challenges was remote turn on and status monitoring of all projectors from the small windowless server/control room. It was essential to control and monitor all networked projectors from this location at one end of the stadium. To overcome this problem, custom software was quickly designed and implemented to graphically illustrate real-time connection, as well as the signal and lamp status of all projection systems. The small room, hidden behind one of the two LED scoreboards, also housed 110 Axon servers that supplied the content to all the projectors. Approximately seven room-sized air conditioners were used to disperse the 35 kW of heat produced by all of this equipment in this small space.

Near the end of the team's stay in Beijing, Sha suggested that the converging light beams from the largest cluster of projectors, as viewed across the stadium, were distracting the view of the upper raceway images. In the design line drawings, the converging beams were most efficient for alignment because angles to reach the screen were reduced. In this case, the artistic direction won over technical efficiency and the staff was asked to move and re-align 18 projectors on one side of the stadium, so at least the VIP side could view the images without the distraction of the bright crossover light. In viewing the live event on HDTV from Canada, it was apparent to members of the team that the beams were diverging in some camera angles and converging in others, especially after the large amount of fireworks added smoke to the air.

Summary

For everyone who attended or watched the Beijing Summer Games Opening Ceremonies on August 8, 2008, as well as the Closing Ceremonies and the September Paralympics Opening and Closing Ceremonies, it was apparent that the production was a resounding success for the Chinese people hosting the Games and the technical teams who were involved in producing what will reign, for some time at least, as the most ambitious outdoor digital video display ever. Though everyone involved in the project struggled with technical difficulties and language differences at times, the spirit of co-operation and the "get it done" attitude were excellent, in keeping with the spirit of the Olympic Games themselves.

To see how the projectors performed at the 2008 Beijing Summer Games, visit: http:// www.christiedigital.com/AMEN/Technology Movies/christieInTheNews/Beijing Olympics2008.htm. •