Behind the Curtain BY JOSH WEISBERG Advanced projection techniques, Part 2—Image tracking and movement A projection technique utilizing location tracking of screen elements has been used infrequently in the past, but is now picking up speed PICTURE A LARGE OBJECT ON A STAGE, perhaps a box or wall with a window. Now, imagine that the box is being used as a screen surface for a projected image, as is the window in the wall. Finally, imagine that the object moves from center stage to stage left and that the image moves with it, as if it painted on the object. That, in essence, is the advanced projection technique of image tracking. The basic technical concept involves creating a projection space (raster area) larger than the scenic object, creating a window within the raster (Picture-in-Picture or PIP) that matches the scenic object and then moving the scenic object in the physical world, while the PIP moves synchronously in the electronic world. Figure 1 illustrates the basic concept. This technique was fi rst used (to the best of my knowledge) for a show we worked on called Sinatra, The Man, His Music , which ran at Radio City Music Hall back in 2006. At that time, the image-tracking concept was signifi cantly challenged by two factors; a lack of a predictable rate of movement for the large scenic pieces being used, as well as the very complicated electronics required to create the PIP windows and move them in a synchronous x/y pattern. We were eventually able to make it work, and when it did it looked fabulous, but it didn’t take long for advances in automation controllers and media servers to make the task much more reliable and simpler to perform. In fact, so much so that only a year later a version of this production in London was accomplished with relative ease and a much smaller complement of gear. Currently, with a few notable productions making extensive use of image tracking, including the current Met Opera Ring Cycle , the technique is having much greater impact in the theatrical production world. What makes this technique so interesting is that it requires a comprehensive bridge between two very separate disciplines— scenic fabrication and projection design— so that the image generating system can locate the scenery in the projection environment and track movement. Our exploration of this technique will begin with this crucial element. Tracking methods The type of movement most common in a tracking system will be along vertical and horizontal axis that correspond with x, y coordinates, see Figure 2 . More complex systems will incorporate the z, or upstage/ Figure 1 – Projected raster with highlighted scenic object FALL 2011 Figure 2 – Illustration showing axis of movement 32 FALL 2011