Professional green & blue screen sets

Tips and parameters for successful studio recordings

We would like to take this opportunity to explain some basic technical terms relating to green screen / blue screen (also known as greenbox / bluebox): The term "chroma keying" is often used as a generic term for this post-production technique. The use of this technique is well known, for example, in weather forecasts, due to the frequent and rapid change of different weather maps. The first cinema film to use a blue screen and the associated technology was "The Thief of Baghdad" in 1940.

Green screen / blue screen technology

The green screen or blue screen technique, often also called green box or blue box technique, is a technique of colour-based image cropping. In principle, the cropping of an image works with every possible colour of the visible colour spectrum in the wavelengths of approx. 380 - 780 nm. However, certain shades of green or blue rarely occur in nature and are therefore good candidates for this technique. There are different opinions as to which of the two colours (green or blue) is better suited for this purpose. Green is less common in clothing than blue and is also almost non-existent in a person's skin colour. In addition, blue eyes can cause irritation. Another argument in favour of green screen is that modern cameras are designed in such a way that each pixel field has one blue and one red, but two green pixel points. The green colour range is therefore recorded and displayed in a much more differentiated way.

Incidentally, other rare colours such as mint or pink could also be used, but green screen and blue screen are primarily used. An image can also be neutralised using different brightness levels. If the background is very brightly lit but the person in front of it is not, the person can also be cropped in this way.

The process of cropping is called "keying", the subsequent combination of the cropped person with the new virtual background film is called "punching". Tips and parameters for a successful green screen / blue screen set:

Lighting

The coordination between people and background is the most important basis for an optimal chroma key. Although the keyers can cope with certain differences in brightness levels, the reflective properties of the material are still important. The background and the person or object in front of it should be illuminated separately if possible so that no shadows fall on the background.

Lighting system / spotlight

The lighting should be as soft as possible to avoid strong contrasts and prominent shadows. Set and background may require separate lamp types (e.g. asymmetrical spotlights).

Colour location

In additive colour mixing, this describes the respective proportion of the colour values red, green and blue (RGB) of a colour in values from 0 to 255. A colour location of 0/177/64 (RGB) is recommended as standard for the green screen and 8/39/245 (RGB) for the blue screen. Keyers are quite tolerant, so they can handle deviations from the recommended colour locations. Pink or mint can also be punched under certain circumstances as mentioned above. To clarify: White has the values (255/255/255) in the colour location in additive colour mixing. When backlighting studio sets using a projection screen in the background, for example the TRANSMISSION rear projection screen with LEDs, the colour location values can be set accordingly on the light mixing console.

Cove

A cove is the concave rounding of an edge. In the green screen or blue screen studio, this transition between the floor, for example made of VARIO CLASSIC, and the back wall, for example made of SUPRA WOOL FELT, is used for soft, edge-free illumination of the background. A coving can be made from various construction materials, often from bent plywood panels that are filled and painted or covered with a textile. For temporary solutions, the textile on the back (e.g. TELEVISION CS) can also be temporarily continued on the floor or "run out".

Luminance - homogeneity

Creases, very different materials on the wall and floor can present problems. Here, for example, the TELESTRETCH offers the possibility of creating completely smooth surfaces, attached to the top and sides of a wooden construction and to the floor with the Gerriets' floor clamping strip. Alternatively, it can also be clamped into a truss frame, in which case the textiles are eyeleted on three sides or all round. Shadows that are too strong and sharply defined also lead to difficulties. The more homogeneous the luminance in the set, the better the key behaviour.

Spill

are reflections or blurring that disturb the image. If a strong light in the green background causes reflections on a person's white clothing, it is difficult to edit the image cleanly later on. To largely prevent this effect, the areas in the green screen that are not required can be covered with black fabric before the photos are taken. Spill also frequently occurs in the outer hair area, as the hair here already has a certain transparency to the background.

Room size

Relationships Too little distance between the people and the background is not desirable. Sometimes, however, the production area does not allow for anything else. This can result in shadows being cast and a spill effect on the people or objects. In small rooms or rooms intended for multiple uses, a track system such as the TRUMPF 95 track system from Gerriets can provide a high degree of flexibility.

Reflective behaviour

Matt and low-reflective surfaces are preferable. They prevent too much light from being reflected onto the set in front of them. However, special attention must be paid to illumination. STAGE MOLTON R 55, STAGE MOLTON CS or SUPRA WOOL FELT are suitable for many applications, but often require separate illumination from the set. TELEVISION CS is easy to handle and can be washed without losing its flame retardancy. However, the nettle fabric can tend to reflect in unfavourable lamp constellations.

TV & STUDIO SUPPLIES

Tips and parameters for successful studio recordings

Green screen / blue screen technology