From creating superheroes flying through the night sky, to dragons attacking villagers, to meteorologists predicting tomorrow’s weather, green screens are common fixtures on set these days. Not just for movies and TV, green screen’s are commonly used in commercials and corporate videos as well. Using green screens, or chroma key screen as it’s technically known, can help you build your next work presentation to crank up sales, train teams, showcase products and much more.
HOW IT WORKS
More correctly referred to as chroma key compositing or simply chroma key, this visual effect is commonly used to add a background that’s not actually there, would be too costly or perhaps dangerous to shoot in, or simply to superimpose a background graphic that would be difficult to film in any other manner.
The principal subject is filmed against a background consisting of a single colour, typically blue or green. This colour is then digitally removed during the editing/post production process. Any parts of the image that are of that colour, are removed and can then be ‘swapped’ with alternate footage.
BLUE OR GREEN SCREEN
So, while ‘chroma keying’ is the post-production work, shooting on a screen on set is the first part of the process. Chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue are most commonly used because they differ most distinctly in hue from most human skin colours. Fun fact - 70% of the human skin tone (of all skin colours) is comprised of red hues.
For many years blue was the chroma key colour of choice in the film era, mainly because it is further from red in the visual spectrum than green. Green however, has become increasingly popular during the digital era, as the image sensors in digital video cameras are most sensitive to green, mimicking the human eye’s sensitivity to green light. These days green is typically used for shooting in studio, while blue is most commonly used outdoors.
Lighting is crucial when using chroma key screens as shadows cast on the screen can affect the final image in a negative way. First the chroma key screen must be properly lit. A perfect chroma screen is evenly lit with no signs of shadows or creases. Next, lighting is set for the talent and props in the scene. It is important that no shadows from objects, people or their movements are cast on the screen during filming! The talented lighting crew at 5Gear ensures all of our chroma key screens are lit in favourable conditions. Colour spill will occur when the chroma key screen reflects light on to the back of your subject, casting a noticeable (typically green) tint. Colour spill is most commonly seen on the back of the shoulders, side of the arms or legs, and through the hair (especially blonde!). Production lighting professionals, known as gaffers, are experts in creating shadowless scenes and preventing colour spill, making them a key person on set when shooting with a chroma key screen.
A perfect chroma key for your production can be a very rewarding final outcome, but it takes seasoned professionals to do it right. Trust 5Gear Studios for your next chroma key green screen project. We have the people and the tools to pull off your perfect visual effect.