It’s time for a break, dear readers; a break from hanging lights, calculating pixels, equalizing the RF mics and tracking down that lost DMX512 universe. When this issue hits the stands, we’ll be deep into the NFL playoff season, and so what better time than now to devote an entire column to a topic dear to our hearts — football and video! Specifically, how are those amazing yellow and blue lines drawn on the field of play? And even more apropos, just how do they move in perfect sync with the cameras? The answer lies in a very complex combination of video, computer and optical technology, and a company of wizards in Mountain View, Calif.
By way of history, several years ago at NAB, three or four companies exhibited a new technology dubbed “ virtual sets.“ In each of these exhibits, an actor moved about a brightly lit stage, painted entirely in chroma-key green, from the floor to the surrounding walls. This was the “real world” portion of the set. However, as you watched the monitors you saw an en-tirely different environment. The actor appeared to be walking within a perfectly realistic room. This was the “virtual world,” and it existed inside a computer.
The key to the realism of the illusion was that the computer-generated room actually panned, tilted and zoomed as the camera followed the actor. This was made possible by a modi-fied camera pan-head and lens that delivered data to a Silicon Graphics Onyx computer the size of a refrigerator. The virtual background was in fact a 3D model, and the Onyx had the horsepower to render the model in real time as the camera moved.
The technology was breathtaking, but cost-prohibitive, and there were very few takers. Keep this little history in mind as we fast-forward to today. You’ll see how that early “virtual set” technology has advanced into the sports arena. But bear with me; it takes a bit of explaining.
I spoke at length with Michael King, field operations manager for Sportvision, the company whose technology is behind those great “first and ten” lines. Based in Mountain View, Cali-fornia, and well into their 10th year of operation, the company is making waves in the industry by enhancing sports broadcasts in several ways.
King explained that the “first and ten” graphics are in fact a three-part equation, and the first part is a precision map of the playing field. “ The great thing about football fields is that they’re a standard size,” said King. “ We use what’s called field generation technology, and using a basic survey laser and a height reader, we take precise measurements of the field, on the edges and in the middle, using the camera location as the zero point. . In this way, we discover the field crown, any undulations and imperfections, and from that we create a very spe-cific field map. ”
In effect, the field map is the “virtual set,” and it’s a highly accurate map — with precision down to 1/1000th of a foot. With the knowledge of where the camera is in relation to that set, we can lock the virtual and real worlds together in real time. “When you break down that data, we create an actual 3D wire-frame of the field,” explained King, “and that allows you to line things up. ”
The second part of the equation is the data. Basically, many professional pan heads are not purely mechanical anymore. With a modern “enhanced” pan head, each time the cam-eraman makes a move, electronic data is created. This data, in turn, provides the instructions that tell the 3D wire-frame how to move — in perfect synchronization with every camera move. The data is sent from the camera back to the television production truck and combined with the camera’s video output.
“We don’t connect the camera directly to our computers,” explained King. “We merge the data and video through separate paths. From the camera’s pan head, we collect pan and tilt data. And from the lens, we collect zoom, extender and focus data — basically, anything that has to do with image magnification. Then, using proprietary encoders, it’s all gathered in a single collection box at the camera location, called an RCS box — Remote Camera Sensor. That information is sent down to the camera truck via an existing audio channel within the cam-era’s triax cable. We actually use one of the un-used microphone channels. In the TV truck, back at our computers, a demodulator turns the audio data back into computer data, which al-lows us to read the data instantaneously as the camera moves and zooms. ”
At this point, we have a 3D map of the field and data from the camera, but we still haven’t drawn any lines. “The last part of the equation is the video,” continued King. “Down that same triax cable, the camera’s video is sent to the camera control unit in the production truck, and they pass that signal on to our computers where the video and data meet. The day be-fore the game, we register the video to the data, and essentially, we line up the real world with the virtual world. ”
Knowing what you know now about the field model (the virtual set), the data, and the registration of the two worlds, imagine a computer system with the power to move that wire-frame “set” in real time and create layered effects in 3D space, and you’ve got “first and ten. ”The field becomes the background layer, the yellow and blue lines are layered on top of the field (in 3D space), and the video from the camera becomes the top layer, spatially on top of the yellow line.
“The part where we actually draw the line is a layered effect that’s keyed under the players, and that’s created in a separate computer we call our matte machine,” said King. “It works on the same principle as the green screen behind the weatherman. We turn the field into that green screen, and it’s up to the Sportvision operator to select the color of the field, and to specifically exclude the colors of players’ uniforms. It’s one of our more advanced features, and it takes great attention to detail — especially if the players are wearing green uniforms such as the Jets or the Eagles, with colors similar to that of the field.”
Finally, the composite signal (including the lines) is routed to the video production switcher, where the technical director (TD) cuts cameras for the broadcast. When the line fades in and out, that effect is being performed by the Sportvision operator — not the TD. But if an error occurs with the Sportvision equipment, the TD has a “clean” version of the camera to take, without the Sportvision enhancement.
Using the same Sportvision technology, we’re now also enjoying team logos and “down and yardage” graphics that are keyed on top of the field (in perfect 3D space), and this technology is also employed in baseball, hockey, and NASCAR broadcasts. Methinks this is just the tip of the video iceberg. For more information about Sportvision, please visit them at www. sportvision. com.
Armed with this knowledge, you can now sit comfortably in your leather La-Z-Boy recliner, remote in hand, and turn to your significant other and proclaim, “Darlin’, you see that yellow line there on the field? I know how it’s done!”To which she’ll reply, “Right, Bubba. Can we watch HGTV now? ”
