Lighting for virtual set

TV&VIDEO: How do you make a virtual composition look real?

Scott Lelieur: There are several factors involved in virtual composition. To achieve the illusion that a real character acts naturally within a computer-generated scene, there are four basic elements: the character's lighting needs to match the lighting generated by the computer graphics. The difficulty with it is that the lighting for the character must be done in such a way as to facilitate the execution of a ChromaKey. That means that you must be very sensitive to the way lighting develops in the virtual world to avoid errors in the coupling of the two elements. Secondly, the matching of the camera perspective in the virtual world must be very accurate with the real-world camera perspective. If the background does not match the camera that covers the character, you will discover their origin. Another important factor is the lack of attention paid to the bright white objects within the scene. It is a frequent problem in lighting for the particular background . Finally, one of the most important elements to create the illusion is the camera movement. It is very difficult to match a computer camera with a real camera. The virtual set technology allows, if you have the right equipment, to have a dynamic camera movement, with the perfect coupling of the cameras in their perspective. It is extremely convincing and helps a lot to make the overall composition look real.

TV&V: What resources do you need for this?

SL: Essentially, the resources needed for virtual set technology are: a properly painted background of a single monochromatic shade such as the digital color blue or green. It requires basic lighting equipment. Video cameras that have the possibility to connect to the system, although not all cameras allow it. A computer or several of them that make it possible and the software for all this to work together.

TV&V: What are the main differences between conventional lighting and lighting for virtual sets?

SL: The main difference is obvious. In a conventional lighting job when a light is directed at a character and a set at the same time, the same light is illuminating the two elements of the composition. In the virtual world or in the world of ChromaKey, light is directed at the character but the scene that will exist is the work of artificial lighting originated in a computer. There is light in reality and there is light in the computer. There is no relationship between them. The goal is to match these two very closely. Within this technique it must be illuminated in the most uniform way possible to achieve the ChromaKey process in a simple way. The balance must be achieved between the lighting needs that make it interesting and the flat and uniform lighting for ChromaKey.

TV&V: What should be kept in mind in the relationship with the virtual set system?

SL: In general, in working with virtual set technology, characters are imposed within computer-generated sets, based on ChromaKey technology. However, one of the tricks to compose, is to define the areas in which the character will not be and on those areas build a lighting that allows to take advantage of the contrast of an illuminated area in which the character is, and another with shadows and brightness to create an atmosphere.

TV&V: Does this change the work of the cinematographer? Do you need special knowledge and skills?

SL: In the fundamental sense you don't change the work of the cinematographer, he continues to be responsible for achieving an image in a particular way. However, it would be helpful if you understood the technology of the ChromaKey. If you understand the best way to illuminate and why some lights might be better than others for a given scene and if you understood the technology of virtual sets well, you would have a huge advantage of what you could do with your equipment in a virtual environment and what you couldn't do in a Blue Screen environment. . It would be helpful if the DP understood lighting work and computer technology.

TV&V: Is it necessary to use a special class of lights?

SL: Computer-generated sets have no lighting considerations. However, if you talk about lighting for the characters, the requirements are exactly the same as those needed for a job in a traditional Blue Screen environment. In other words, lights are needed for the character, floor, background, and setting objects, depending on ChromaKey's technology. The character is illuminated first and then additional lights can be added to create shadows on objects and in places where the light is not bright. All these lights are conventional except if fluorescent lights are used where the frequency of video capture must be controlled. There are no specific lighting requirements. Another possibility is to connect a robotic lighting system to the virtual set software which would give enormous potential. It would have the advantage of precision that gives the control of all the elements by the software.