The impressive fireworks display included a series of 29 giant footprints, made of white starbursts, that seemed to traverse the sky from Tiananmen Square to the Olympic Stadium. But the TV presentation of the fireworks, broadcast to the world as well as shown on the giant screens within the Olympic Stadium, included not the actual event but rather a 55-second digital film of the 29 footprints, complete with simulated camera jitter and haze, seamlessly inserted into the broadcast.

Representatives of the Beijing Games have stated that the digital trickery was necessary because the actual effect would not have been clearly visible in the prevailing atmospheric conditions, while filming it from the air would have endangered the helicopter pilot. Here, the artist himself responds to the controversy:

The explosion event Footprints of History: Fireworks Project for the Opening Ceremony of the 2008 Beijing Olympic Games consisted of a series of 29 giant footprint fireworks -- one for each Olympiad -- over the Beijing skyline, leading to the National Olympic Stadium. The 29 footprints were fired in succession, traveling a total distance of 15 kilometers, or 9.3 miles, within a period of 63 seconds.

It is quite customary to prepare a backup reel for major televised events of this scale, and this has been true of the opening and closing ceremonies of previous Olympic Games. We were aware of this and thus created our own reel from dress rehearsal footage of the footprint fireworks. The sequence was then created using computer graphics.

From my own perspective as an artist, there are two separate realms in which this artwork exists, as two very different mediums have been utilized. First, there is the artwork that exists in the material realm: the ephemeral sculpture. This was viewed by people attending the ceremonies inside the stadium and standing outside on the streets of Beijing. This artwork was documented from various vantage points on video, which has been broadcast by many international media outlets.

Second, there is a creative digital rendering of the artwork in the medium of video. It is a single version of the event viewed by a large broadcast audience. Such a conceptual work can exist simultaneously in these two separate realms. And perhaps to also take Footprints of History into this second realm was necessary because in many of my explosion events, such as Project to Extend the Great Wall of China by 10,000 Meters, the very best vantage point is not the human one.

CAI GUO-QIANG was director of visual and special effects at the 2008 Summer Olympics in Beijing.