Elements like scanned film or video, which are called plates, are placed into to composites. Also stills like photos, drawings or mattepaintings can be part of a compositing. Computer generated images (CGI) are also very commonly used to create fantastic environments. The main element or even the most important kind of tool to integrate images into another is the matte – manual created or generated automatically.

Before computers were able to handle imagedata, the process of compositing was handwork. In this article I would like to concentrate on compositing with computers. Since computers have softwaresolutions to manipulate moving pictures compositing became a major part of postproduction.
Laptop screen superimposed over a blank original

A simple compositing can already be a picture in picture image creation. Also a graphic animation with text and a background can be considered a compositing. Although mostly refered to motion graphics. The complexity starts at a very low level and anybody that used photoshop already did a compositing. The basics in photoshop are the same as they are for image sequences.

Colorcorrection is also part of standard compositing, although it is not really the combination of different kind of image but it is a very important toolset for a compositing artist.

Classic compositing can be seen in movies like Titanic, Jurrasic Park, Matrix, Hulk or Superman. Many different plates and CG Images have been combined in those movies to create a new exciting image sequence. The best effects are the ones you do not see – which is sometimes frustrating for compositing artist but is also a big reward if nobody has noticed that most part of the pictures has been artifically created.

The result of a compositing is a visual effect – VFX. VFXs are part of the special effects. All effects that can be achieved while filming like explosions, lenseeffects or backprojections are called practical effects. However, practical effects in credits of feature film movie are often called special effects. Its just a therm, so I do not want to be picky. And one more thing: Explosion, lenseeffects or backprojection can of course also be created in 3D with e.g. particles. However always do as many effect in-camera, they are probably more convincing and more cost-effective.
Different passes for compositing

As stated at the beginning the basic element is the combinations of layers with somekind of blend mode or stencil mask, matte, transperency channel or alphachannel. Often information beyond the given image has to be provided to do a convincing compositing – especially important for classic compositing. Therefore different passes are recorded while shooting with e.g. a motion control camera. Passrendering is also done within 3D animation work. Passes like shadowpasses, highlightpasses, volumelightpasses, beautypasses etc. It gives the artist the best control over several parameters. Information about the lighting situation, the distance of the object to the camera as well as the reflexionenvironment has to be considered when combining all elements into a perfect composition. The perspective has to be perfect. The light should be set on the elements as desired and color should match throughout the new picture.

Main function used while doing compositing are keying, tracking and stabilzing, colorcorrection, rotoscoping and filtereffects like blur, glow or seldom emboss.

Special software and/or hardware has been devoloped to achieve those amazing effects reaching from simple camera rig removal to science fiction world crowded with futuristic cars and aliens. The power of those systems differ in detail. All of them have one thing common: They combine and manipulate digital images. To find the correct solution, systems should be checked on every detail. There might be differences between the keyer, or the user interface. Functions might be missing or they might be better than in other systems. Always consider the problem of getting different kind of footage into the machine and out of the machine. The philosophy might be node based or layed based or even both. The prize reaches from freeware to more than a million euros. Support and the user community are always also very important to take a look at.

Deciding on one tool is never easy, but knowing many systems is always an advantage. There are standard tools in the industry and there are underdogs, but you never know what will be in the future. But never forget they are just tools. The artist has to have the talent and skills. Any UI can be learned within weeks. Knowing the basics and having the talent and drive are the keys for being a successful composititing artist.

Written by Axel Gärtner

Sources:
Ron Brinkmann: The Art and Science of Digital Compositing. Morgan Kaufmann
Thomas Mulack / Rolf Giesen: Special Visual Effects. Bleicher Verlag, Gerlingen.
Axel Gärtner: „Programmierung eines VR-Postproduction-Moduls für Maya 2.5 in der Skriptsprache MEL für den Import und die Weiterverarbeitung von Trackingdaten aus dem ORAD-Cyberset-System“. Diplomarbeit. TU Ilmenau, 2000.