Finishing Post Creative
The Ins and Outs of Virtual Sets
Virtual sets have been around for a long time, in the sense that techniques that allow an actor to be filmed in one location, but be made to appear in another onscreen, were developed in the early days of cinema. Advancing technology, however, means that the possibilities are expanding as fast as the cost comes down. The technique is known by a variety of names: 'keying', 'chroma-keying', 'blue or green screen', 'Ultimatte' or, more descriptively, 'Colour Separation Overlay' (CSO).
Filming in the studio has essentially remained the same. Actors are shot in front of a uniformly coloured background - usually a cloth or screen - with blue and green the most common colours, although in theory any colour can be used. What's important is that the background colour isn't found on the actors' clothing or props, or else those parts will appear with the background superimposed over them. Conversely objects can be covered with this colour in order to deliberately hide them. To create the illusion of an object floating in mid air, the stand it rests on can be wrapped in blue cloth.
Before the rise of CGI there were severe limitations to what could be convincingly accomplished with CSO. The camera had to be locked in place because there was no way of synchronising the movements of the foreground and background to a realistic degree. It was also difficult to make objects in the foreground look as if they were truly inhabiting the scene, because the things which the eye takes for granted - shadows, reflections and nuances of lighting - were absent.
Today, virtual sets are able to solve these problems. The set is modelled three-dimensionally in a computer, and images of it can be rendered from any conceivable angle. When the actors are being filmed in the studio, a special system stores the movements of the camera, and this data can be used to ensure that the perspective of the CGI background stays in unison with the forground at all times. Pans, zooms, tilts and even handheld cameras can then be used, allowing as much freedom of filming as a conventional shoot.
Pictures 1 and 2 on the right are taken from a 'Noddy ABC' TV commercial, before and after the virtual set was added. While the edges of the original shot are not covered by bluescreen, this is unimportant as long as none of the foreground action takes place here. These areas can simply be 'blocked off' and covered with the background in the final picture.
In pictures 3 and 4, from a Reader's Digest commercial, we can see how the size of a virtual set can be much greater than the size of the actual studio the footage was filmed in. The original shot is reduced in size and placed in the centre of a much larger virtual set. Notice also the computer-rendered reflection of the presenter on the floor.
We can quickly see from these examples why a virtual set can be so cost-effective. Building a real-life set to these designs and dimensions would not only be expensive in themselves, it would require a very large studio to film in and high storage costs for sets between shoots. In contrast, virtual sets take up nothing but space on a hard drive. And virtual sets are capable of things that would be impossible for a conventional set, as shown in the set used for our 'Encyclopaedia Britannica' commercial (picture 5)
Sample Images
Click on any of the thumbnails below to view a larger vesion
- 1. Noddy ABC
- 2. Noddy ABC
- 3. Reader's Digest
- 4. Reader's Digest
- 5. Encyclopaedia Britannica
- 6. Reader's Digest
- 7. Boots Q3
- 8. Boots Q3
