Compositing

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Compositing ( English for composition , mixture ) is a term used in video and film technology and takes place in the post-production of a film as a visual effect application. In compositing, two or more separately recorded or created elements are merged into one image. In computer graphics , compositing refers to the joining of several layers of a volume, one behind the other .

Compositing is the process of merging several image elements into a coherent overall picture. The most important techniques are cropping (by keying or rotoscopy ), the photo-realistic integration of cropped footage , rendered images or matte paintings, and the temporal change of footage (retiming).

The corresponding job title is the compositing artist .

history

In the 1930s, the first special effects were using a optical bench ( optical printer ) and a traveling matte realized. An optical printer was used to copy film material: it consists of a projector that projects the film and a camera that films it again. With the help of a traveling matte (English: moving mask), parts of this projection were initially shaded, which left unexposed areas in the film material. In a second run, the inverse mask was used to insert a second film material in the shaded areas without double exposure of the previously exposed areas. However, the image quality also suffered from these mechanical processes, which is why it was usually only used for a short time and could not be repeated as often as desired.

In 1940 Lawrence Butler expanded this technique and invented a way of photochemically producing traveling matt moving objects. He was awarded an Oscar for this invention of blue screen technology . Until the 1990s, this compositing technique was the only way to efficiently release and assemble moving objects.

Refinements to this technique were first used on a large scale in the 1982 film Blade Runner , which combined numerous takes of miniature models, matte paintings , rain and real film recordings.

With the movie Indiana Jones and the Last Crusade (1989) this technique was first generated in the computer. For this purpose, the film material was digitized, combined using image processing software and then transferred back to film material.

From the mid-1990s, compositing was also used to insert digitally generated characters into real-life recordings (e.g. Jurassic Park (1993), Godzilla (1997)).

A well-known company in this area is Industrial Light & Magic by George Lucas , who made the visual effects for Star Wars , Jurassic Park , Abyss , Terminator , Star Trek and Indiana Jones , among others .

techniques

Clipping

The clipping of elements is one of the most important areas of compositing. Isolated images and film sequences can be edited, changed and recombined individually. The main techniques used are keying and rotoscopy . The aim is to create an alpha mask that exactly matches the image . Particular difficulties arise when cropping semi-transparent objects, blurring and hair.

Photorealistic integration

A common goal is to add new elements to existing image material ( footage ). These elements include cropped images, matte paintings , or rendered elements . The aim is to create a realistic look and to make the inserted elements look as if they were filmed by the camera . Important aspects of integration are the correct perspective and (with a moving camera) parallax , color and brightness adjustment to the footage, and correct blur ( defocus ) and motion blur ( motion blur ). The creation of camera peculiarities such as grain or image defects such as chromatic aberration , distortion or edge light drop also ensures optimal integration when it is adapted to the original footage.

software

Specialized program solutions exist for the application of compositing in the professional field . These can be roughly classified into two categories with regard to their user interface : node-based compositing software and layer-based compositing software.

Examples of compositing programs include:

as well as the open source programs:

The open source video editing program Cinelerra for GNU / Linux also has tools for compositing. Today all professional non-linear editing programs (such as Avid, Media 100 or Final Cut Pro ) have compositing capabilities.

An important part of compositing programs are expansion modules that increase functionality. These include:

  • Boris / FX
  • Sapphire
  • Crocodile
  • monster
  • Fresh air
  • REVision
  • Furnace

Volume graphic

Front to back compositing : From the viewer's point of view, the colors are offset against each other in layers depending on the transparency.

In direct volume visualization , compositing is used to combine several layers of a volume one behind the other to form a 2D image. The entire volume can be imagined as a multitude of volume cells ( voxels ), which are transparent and emit light of a certain color. The color and transparency values ​​must be offset against each other along a "line of sight". The methods used for this provide different results:

  • Average : The color is simply averaged over all voxels through which the line of sight passes. The result is similar to an X-ray.
  • Front to back : The voxels are traversed by the viewer towards the background. The previous transparency along this route is always multiplied by the transparency of the current voxel. The color of the voxel then flows into the overall color depending on the transparency. Since the transparency lies in the interval , it becomes smaller and smaller. The color of the voxels further back is hardly included in the overall color, so that the algorithm can be terminated if the value falls below a certain threshold value . This increases the rendering speed significantly.
  • Back to front : The voxels are passed through from the background to the viewer. The color value calculated for the previous voxel must be offset against the transparency and color of the current voxel.

In addition, a binary tree can be used with all methods, which divides the line of sight into several segments. These can be calculated in parallel and later reassembled to achieve a further gain in speed.

literature

  • Ron Brinkmann: The Art and Science of Digital Compositing . Morgan merchant. ISBN 0121339602 (English)
  • Steve Wright: Digital Compositing for Film and Video . Focal Press. ISBN 0240804554 (English)
  • Patricia D. Netzley: Encyclopedia of Movie Special Effects . Oryx Press, Phoenix, Arizona 2000 ISBN 0-816-044929 (English, p. 47)
  • Thomas Mulack, Rolf Giesen: Special Visual Effects . Bleicher Verlag, Gerlingen ISBN 3-88350-911-6

Web links

Wiktionary: compositing  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ Compositing Artist. Retrieved February 14, 2017 .
  2. ^ Optical bank - Lexicon of film terms. Retrieved March 25, 2017 .
  3. ↑ Jeffrey A. Okun: The VES handbook of visual effects . S. 551 .
  4. ^ Steve Wright: Compositing Visual Effects .
  5. ^ A b c Michael Bender and Manfred Brill: Computer graphics . An application-oriented textbook. 2nd Edition. Hanser, Munich 2006, ISBN 3-446-40434-1 .
  6. ^ Stefan Gumhold: Scientific visualization . Volume visualization II. 2009 (lecture slides).
  7. ↑ a b c Stefan Wesarg: Medical Visualization. (PDF; 2.4 MB) (No longer available online.) May 18, 2009, archived from the original on June 13, 2010 ; Retrieved September 6, 2009 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.gris.informatik.tu-darmstadt.de
  8. ^ Charles D. Hansen and Chris R. Johnson: The Visualization Handbook . Elsevier, Burlington 2005, ISBN 0-12-387582-X .