Application of camera trajectory tracking technology in film and television production

Application of camera trajectory tracking technology in film and television production

In film and television production, it is often necessary to calculate the camera motion of the real shot picture, that is, the camera motion trajectory tracking technology, when combining the real shot picture with the three-dimensional special effects scene made by computer. The following is my search about the application of camera trajectory tracking technology in film and television production for reference and reading, hoping to help everyone! For more information, please continue to pay attention to our fresh graduates training network!

With the development of film and television post-production technology, the audience can see various special effects scenes in film and television works. Among them, camera trajectory tracking plays an important role in special effects scenes. Most special effects production needs camera trajectory tracking (hereinafter referred to as lens tracking) after shooting. Its purpose is to create an environment for post-production, where computer-generated three-dimensional materials can be integrated into real shots (and vice versa), so that the actions of computer-generated robots or creatures can be combined with real shots and look like real performances.

First, the principle of camera trajectory tracking technology

The use of lens tracking technology was initiated by george lucas and other stunt pioneers in 1970s. It was originally a mechanical tracking system. In 1990s, due to the rapid development of computer technology, reverse tracking technology of camera motion trajectory came into being. Both of them are used to solve the problem that two-dimensional image tracking technology can only track the subject, but it is also a major movement for film photography. Limitation of camera movement and its solution. In the production of three-dimensional special effects movies, the first thing to do is to trace the computer-generated three-dimensional material to the real shot. This technology solves the problem that two-dimensional picture tracking can not be used for three-dimensional tracking synthesis, and makes the camera motion matching function in the whole digital stunt synthesis technology tend to be complete.

The principle of camera trajectory reverse engineering technology is that the computer obtains the position information and depth relationship of the original scene in the virtual three-dimensional coordinates through pixel detection and motion analysis of elements in the two-dimensional picture, and then finds out the camera trajectory during the original shooting by constructing the three-dimensional virtual shooting scene. Once the original motion trajectory of the camera is simulated through operation, when the computer-generated 3D graphics need to be synthesized into the real shot screen, the virtual camera set for the 3D computer graphics can move synchronously with the original camera, so the synthesized scene can follow the real shot scene seamlessly.

Imagine a typical special effects shot: the director wants to get a scene in which a CG monster breaks through the window of a building, crosses the street and enters an alley. Because CG monsters will interact with the windows of the building, the special effects director will ask for a three-dimensional simulation of the real broken window effect. On the day of shooting, the director will consider the scene and lens position in this special effect shooting from an artistic point of view, such as how to consider the position of the building broken by the monster in the picture, even if there are no windows when shooting on the spot. Directors and photographers will practice the camera movements many times before the official shooting and imagine the scene of monsters crossing the street. When the director is satisfied with the lens, it will be digitized and handed over to post-production to add special effects. When the post-production team receives the film, it needs an animator to debug the monster's movements and a technical director to deal with the special effects of broken windows. Before this, the camera tracking engineer must match the moving pictures in advance. Engineers must ensure that the trajectory of the real camera is exactly the same as that of the virtual camera in the three-dimensional scene. Considering that the window needs to be smashed by the monster, if its perspective position in the film does not match the three-dimensional scene, for example, when the lens moves to the left, the window still stays in its original position, obviously the lens is broken.

Second, the application process of camera trajectory tracking technology

Combining computer-generated materials with real-life shots is a very important technology for related industries such as movies and virtual reality. From the lens tracking engineer's point of view, when shooting a scene, the camera is basically doing one thing: converting the three-dimensional space it shoots into a two-dimensional plane. The purpose of lens tracking is completely opposite. Engineers need to restore the three-dimensional scene shot by the camera through accurate calculation of software and simulate it in the computer, and the key to connect the two is the camera.

There are many ways to track the lens. First, we evaluate the movie clips that need to be tracked in order to choose the best tracking scheme. Many times, this process is omitted, and it is likely that more time will be spent in the later process. Then, the camera tracking software (or motion matching software) is added with the previous shooting parameters for matching operation, mainly including lens focal length, recording frame rate and motion mode, so as to restore the real shooting scene more accurately, just like logical reasoning. More information can make the process simpler.

Five or six years ago, lens tracking engineers needed to consider all the internal and external factors of camera movement and choose different tracking methods for different occasions. Now with the development of science and technology, tracking software uses a method called? Photogrammetry? Technology has greatly improved the intelligent tracking level of software. The moving virtual camera and three-dimensional scene data can be obtained through software operation. After that, engineers reconstructed the three-dimensional space on the two-dimensional plane according to these data, such as building the two-dimensional building and the road in the film in three dimensions, thus completing the tracking.

The next step is the most important link. Engineers need to test whether the tracked lens is true to the real shot, and whether the created three-dimensional space and virtual camera match the real world perfectly. At this point, use tracking software to place your test object in the reconstructed three-dimensional space. Failed tracking is often obvious, for example, the test object drifts or shakes during playback. It is necessary to repeatedly test whether the tracking is successful, because the failed shot tracking will always be used in the post-production pipeline, and will not be found until the final synthesis output. This situation is terrible. Special effects artists and animators have to change their special effects again, and the time and energy spent will put great pressure on the production cycle of a film.

Finally, the tracked scene file is handed over to other artists under the workflow. It usually includes the coordinates and size of the three-dimensional scene, the necessary roles and facilities, and reasonable naming rules. An orderly tracking file can provide convenience for other artists who take over the processing, and at the same time, the tracking engineer does not need to explain it to them in detail afterwards, saving a lot of unnecessary time.

To sum up, the important reason why camera trajectory tracking technology occupies a place in special effects scenes is that a basic problem to be solved when digital technology is applied to film special effects is the tracking and matching of camera trajectory in motion shots. In special effects movies, if you always use fixed lenses, it is not easy to achieve the artistic effect pursued by the film. The special effects synthesis of shots is to integrate computer-generated materials from different sources into real shots in a correct and true way.

To sum up, camera trajectory tracking technology has a decisive impact on this industry. The audience in the cinema are enjoying the wonderful special effects, but they may not notice the work of the film and television special effects artist. It is the efforts of these obscure lens tracking engineers that determine the effect of these stunts. They let the audience see all the special effects, which is an indispensable part of shooting.

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