page_title: Chroma key
section_title: Processing a green backdrop
hierarchical_section_title: Chroma key / Process / Processing a green backdrop
caption_attribution_description: Deutsch: Virtuelles Fernsehstudio des Saarländischen Rundfunks in Green-Box-Technik English: Virtual television studio with chroma key technique (green-screen), located at Saarländischer Rundfunk Français&#160;: Studio de télévision en technique d'incrustation (lieu: Saarländischer Rundfunk)
context_page_description: Chroma key compositing, or chroma keying, is a visual-effects and post-production technique for compositing two images or video streams together based on colour hues. The technique has been used in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture, and video game industries. A colour range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as colour keying, colour-separation overlay, or by various terms for specific colour-related variants such as green screen, blue screen and magic pink; chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from human skin colours. No part of the subject being filmed or photographed may duplicate the colour used as the backing, otherwise, the part may be erroneously identified as part of the backing.
context_section_description: Green is used as a backdrop for TV and electronic cinematography more than any other colour because television weather presenters tended to wear blue suits. When chroma keying first came into use in television production, the blue screen that was then the norm in the movie industry was used out of habit, until other practical considerations caused the television industry to move from blue to green screens. Broadcast quality colour television cameras use separate red, green and blue image sensors, and early analog TV chroma keyers required RGB component video to work reliably. From a technological perspective it was equally possible to use the blue or green channel, but because blue clothing was an ongoing challenge, the green screen came into common use. Newscasters sometimes forget the chroma key dress code, and when the key is applied to clothing of the same colour as the background, the person would seem to disappear into the key. Because green clothing is less common than blue, it soon became apparent that it was easier to use a green matte screen than it was to constantly police the clothing choices of on-air talent.   Also, because the human eye is more sensitive to green wavelengths, which lie in the middle of the visible light spectrum, the green analog video channel typically carried more signal strength, giving a better signal to noise ratio compared to the other component video channels, so green screen keys could produce the cleanest key. In the digital television and cinema age, much of the tweaking that was required to make a good quality key has been automated. However, the one constant that remains is some level of colour coordination to keep foreground subjects from being keyed out.
caption: Virtual television studio with green-screen technique. The high amount of contrast between different parts of the screen is not ideal (see even lighting). Green reflections from the desk would create undesirable artifacts.
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