The basic idea of “green screen” or “chroma key” photography is simple: take a photograph of a subject in front of a ‘green screen’ and then digitally remove or ‘key out’ the green. The ‘keyed out’ areas become transparent and when ‘merged’ with an alternative background image, the background scene ‘shines through’ the keyed out areas and becomes visible. The technique has been used by the likes of Hollywood and the BBC weather team for donkey’s years [...]