3-D Motion Tracker
Motion tracking is the foundation upon which all live-action visual effects are built; this is the first step in creating a match move, which allows a computer-generated object to be inserted into live-action footage.
The 3-D motion tracker works as a member of the visual effects team during post-production and is responsible for identifying and tracking features in a scene that will later include CGI objects. He or she typically works under the direction of the visual effects supervisor and a senior artist. To begin, the motion tracker uploads a selection of footage to a software program like PF Track. Next, he or she must determine if and where masks should be applied within the frames. Masks, as the name indicates, effectively hide information from the program that should not be tracked. For example, if the scene includes an actor moving about a room, the motion tracker may wish to hide that actor in favor of tracking the stationary furniture within the real space.
The key task of motion tracking is setting points, which represent 2-D coordinates within each frame. The software program uses these coordinates to determine and track the camera’s position throughout the scene. The artist selects stationary points within the space that represent real objects and where there is a high degree of color contrast—corners work especially well. Many software applications will offer the option to automatically place points based on color contrast information. In this case, the artist reviews the points through the progression of frames and then deletes any errant points that are misplaced or unnecessary. The technique of interactive tracking requires the artist to place points by hand in each frame in order to create an effective track; this is sometimes necessary in footage that includes a great deal of object movement or camera jitter in the sequence.
Once the points are set to the motion tracker’s satisfaction, he or she allows the program to calibrate in order to solve for 3-D motion. Because video footage represents a series of 2-D images, the software applies an algorithm that will make it possible to treat each frame as a 3-D space when inserting three-dimensional objects. CGI objects will then be augmented to reflect the camera’s movement through the scene, accurately reflecting perspective, size, and distance relative to the camera and real objects in the scene. The artist must also establish a ground plane that tells the software where the spatial axis of the environment within the frame is; this orients the virtual camera and selected points in a definite space. At this point, the motion tracker will typically export the completed frames to a new program like Maya where the 2-D frames are reconstructed by a match mover to represent a 3-D environment, and the computer generated objects are placed within the scene.
Skills & Education
A career as a 3-D motion tracker requires training in visual effects techniques and appropriate software. A college degree in computer animation or related field is the typical path toward employment. Visual effects artists, whatever their specialties are, must have a solid education in composition, lighting, perspective, and similar artistic aspects of cinematography. While the computer lifts most of the burden of mathematical calculations off the artist, it is beneficial to understand the algorithms at work in the motion tracking process. The techniques of the craft are constantly evolving and becoming more sophisticated, so the more the artist grasps of the equations involved, the more he or she is able to contribute to the advancement of motion tracking in cinema.
What to Expect
The role of the 3-D motion tracker is considered an entry-level position within a visual effects studio. A rookie may be recruited directly out of college based on his or her VFX reel or may graduate to the role from that of render wrangler. On the job, the work of the other artists and animators further down the post-production pipeline is dependent on the motion tracker’s initial process; this means the artist must show a keen attention to detail and a meticulous work ethic. A motion tracker who can deliver clean tracks efficiently will prove invaluable to the studio, thereby moving another step closer to promotion. Career advancement will depend on your specific skills and artistic or technical talent, but related careers include rotoscope artist, match mover, lighting artist, texture artist, and animator.
Have some feedback for our editors? Contact Us