Introduction of Tracking Technology in Film and Television Post-production

Introduction of Tracking Technology in Film and Television Post-production

The rapid development of film and television technology has brought unprecedented visual feast to the audience. From movies to analog TV, to digital TV, and now to 3D cinema, the clear and vivid pictures, shocking effects and sensory enjoyment are amazing. Watch the introduction of tracking technology in film and television post-production with me, hoping to help!

With the rapid development of film and television technology, the later film synthesis technology has also been promoted and developed. It is a new discipline, and it is the synthesis of traditional film and television technology, digital film and television technology and computer technology. Its appearance is the inevitable result of scientific and technological progress and the inevitable demand of the public for high-level pursuit of film and television works. Digital film, TV column packaging, advertising production, film animation, online games and other fields have all been applied to the post-film synthesis technology.

Through the later film synthesis technology, producers can create all kinds of imaginary images and animations, and easily reproduce ancient creatures and natural phenomena that cannot be realized due to objective factors, such as dinosaurs, alien creatures, cosmic planets and so on. , enriched the audience's image space and broadened their horizons.

1, the basic meaning of post-film synthesis

Film and television post-synthesis is divided into post-production and special effects production, and post-production is divided into linear editing system and nonlinear editing system. Linear editing is a way to edit tapes. It is a technology to connect the material into a new continuous picture by electronic means according to the requirements of the program content. Combinatorial editing is usually used to edit the material into a new continuous picture in sequence. The disadvantage is that the material cannot be accessed randomly; After repeated copying of analog signals, the signal attenuation is serious and the image quality is degraded. You cannot insert or delete semi-finished products at will; More equipment is needed, and the installation and debugging are more complicated; It is difficult for creative people to exert their creativity.

Non-linear editing mainly completes digital production with the help of computers. It uses hard disk, magnetic tape, audio information and other media to store information at will. The information storage is parallel and has nothing to do with the practice of information reception. Nonlinear editing integrates video recorder, switchboard, digital special effects machine, editing machine, mixer, MIDI creation and other equipment. Generally speaking, nonlinear editing has the advantages of high signal quality, high production level, cost saving, investment protection and networking. Nonlinear editing technology has become the mainstream technology of film and television program production.

Film and television synthesis technology is a kind of technology to synthesize various pictures and effects, which refers to the use of special technical means to express scenes that normal means and technology can not achieve, also known as special effects or stunts. Usually, models, special animation software and other means are used to express the characters and scenes needed for the plot, such as simulating natural phenomena such as plane collision, star explosion, clouds, rain and snow, and also realizing stories and scenes with sci-fi colors such as character deformation and biological variation.

There are good kinds of post-film synthesis software, such as three-dimensional character scene animation, particle system, multi-layer synthesis and special effects. This paper focuses on multi-layer synthesis and special effects software, such as Adobe After Effects, Combustion, Shake, Vegas, VideoStudio, Premiere, Edius and so on. Post-film synthesis is divided into two parts: video synthesis and nonlinear editing, both of which are indispensable. Video synthesis is used for artistic combination and processing of many different elements to realize special effects, editing and opening animation, while nonlinear editing can realize random access to digital media, non-sequential recording or playback editing. AE is good at video synthesis. In particular, AE tracking technology is the most common in many kinds of film and television special effects.

2. Introduction of tracking technology

Post-film synthesis mainly includes three important technologies: keying, color matching and tracking. Here we mainly study the application of tracking technology in post-editing synthesis. In a picture scene, we can use Photoshop plane synthesis tools to complete the synthesis through keying and color matching; In video scenes, the background is often moving, so we need to use tracking technology to track the movement of the background. Tracking technology, as its name implies, is to follow the content on the screen.

Tracking is the process of selecting a feature area (sometimes called a tracking point) on the screen from a series of images and analyzing it automatically by the computer. The position of this feature area changes with time. The result of tracking is a series of displacement data. Generally speaking, the software will let the user specify a rectangle. Area as a characteristic area. This area should meet the following conditions: the pictures in the area have obvious differences in color or brightness, the shapes of objects in the area have no obvious changes, and the objects in the area will not be blocked by other objects for a long time.

This feature area is convenient for software to search and find, and at the same time, the software will not lose track because of being blocked. The software will also let users specify a search area, which is larger than the feature area and should include the range where the feature area appears in the next frame. In the next frame, the software will find the position of the feature area in the search area, calculate the displacement, and automatically set a new search area for the next frame according to the new feature area position. Using this search area, the software can limit the search to a small range without searching on the whole screen. This not only improves the search speed, but also reduces the possibility of errors. However, the scope of the search area must be set correctly. If it is too large, the search efficiency will be reduced. If it is too small, the feature area may move out of the search area, resulting in tracking failure.

The most common use of these displacement data is to paste the object in another picture to the picture just tracked according to this changed position; You can also use this data, such as adding spotlights to buildings. By moving the tracking picture in the opposite direction by the corresponding distance, we can offset the movement of the original lens and keep the feature area in the original position on the picture, just as the camera is fixed. This is called stability. Tracking and stabilization using only one feature area is called point tracking, which is the simplest tracking situation because this tracking can only get displacement information. However, the motion mode of the camera lens is far from simple: the push-pull and zoom of the lens will enlarge and shrink the image, and the rotation of the lens will rotate the picture.

You can't get this kind of information with a little tracking. However, if two feature areas with the same relative position on the screen are tracked at the same time, and two position points are obtained, the enlargement and reduction of the screen can be inferred from the distance change between these two points, and the rotation of the screen can be obtained from the angle change of the connecting line between these two points. So two-point tracking goes further than one-point tracking, and we can get the information of screen enlargement and rotation through it. The movement of the lens often causes changes in the perspective of the picture. For example, when the camera rotates around the computer display, the viewing angle of the display will change.

If we track four points on the screen at the same time, we can simulate this change of perspective and paste a picture on the monitor screen accurately, which is four-point tracking. Of course, the picture changes brought by camera movement are far more than that. At present, the newer software introduces multi-point tracking, and the actual motion trajectory of the camera can be accurately obtained by analyzing the motion of a large number of tracking points. For a two-dimensional picture, it is almost impossible to reproduce the various changes caused by the complex motion of the camera, but for a three-dimensional software, this camera trajectory can be used to control the virtual camera, so that the three-dimensional generated image coincides with the motion of the real camera, thus facilitating synthesis.

3. The application of tracking technology

In order to facilitate the later tracking processing, we must design the movement of the lens and arrange the tracking points according to the tracking needs before actually shooting the material of the synthetic lens. Sometimes the high reflection almost naturally formed on the screen can be used as a good tracking point, such as the corner of the building and the conspicuous signboard on the distant wall. Sometimes you have to set your own tracking point, such as drawing a brightly colored cross at the location to be tracked, or fixing some objects such as balloons. The principle is: firstly, the tracking point should be in sharp contrast with the surrounding images; Secondly, the shape of the tracking point should not change with the movement of the lens; In addition, enough tracking points should be arranged. When the lens moves, some tracking points will move out of the picture or be blocked. There should be enough other tracking points at this time to ensure that tracking can still be carried out. When setting tracking points, we should also pay attention to the fact that the tracking points that are generally set manually must be removed from the final composite map. If the composition happens to be covered by foreground objects, it is best. If it doesn't work, it may have to be removed by manual picture repair. If so, when setting the tracking point, we must also consider that it is easy to maintain in the future and will cause too much trouble. A little tracking is common in science fiction films, such as the movement of flying saucers and flames; Two-point tracking is common in pendulum, chase and other scenes; Multi-point tracking is common in complex scenes such as photo album flipping. The application of tracking technology makes the creators create more exquisite and shocking film and television pictures, which greatly inspires the creators' creative inspiration.

In a word, the tracking technology in film post-synthesis greatly facilitates the later film creators to create better film and television effects, and can give full play to the creators' rich imagination and creativity according to the needs of the plot. The application of tracking technology in film and television post-synthesis greatly improves the work efficiency of creators and lays the foundation for creating high-quality film special effects.

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