Research and Understand Green Screen

1) A green screen is often used when creating television programmes and films, it's also known as Chroma Key. Green screens are used as a background which actors are then filmed in front of so that they can later use computer softwares to add in a scenery or some kind of imagery. Literally anything can be added in with it, so they could use it to show people at, for example, the Antarctic or in a busy city like New York. Sometimes they are used because either they want to show people flying or a city on fire which is impossible to do in real life. They also do it because sometimes it's more hassle to corner off an area to film in a public place, so it's easier and probably cheaper to just use a green screen.

2) History of Green Screening:
Before digital composing was invented, a time consuming process called 'Travelling Matte' was used in film making. In 1930 the green screen method was developed at RKO Radio Pictures. Linwood Dun, of RKO, used an early version of the travelling matte to create 'wipes' in which they used transitions like a windshield wiper in films such as 'Flying down to Rio' (1933). The first use of the proper green screen process to create travelling matte was used for the film 'The Thief of Bagdad' (1940) where they had a scene of a genie escaping from a bottle. Larry Butler was credited for the development of the green screen. Arthur Widmer, a Warner Brothers employee and ex-kodak researcher began working on an ultraviolet travelling matte process and then went on to develop more techniques for the green screen. A drawback to the traditional travelling matte was that the cameras shooting the images to be composited cannot be synchronised very easily. For a long period of time, some matte shots had to be done 'locked down' so that neither the matted subject nor the background were able to shift their camera perspective at all. Eventually, computer timed, motion-control cameras reduced this problem, this meant that both foreground and background could be filmed with the same camera movement.
Georges Melies used the matte shot which was the first compositing technique, for his film 'four heads are better than one'. To do this he would black out part of the frame using a piece of glass with black paint on it, this means that no light would get underneath so it wouldn't get exposed. Then he would rewind the tape and matte out everything else and expose only the part of the frame that was under the matte earlier meaning it can combine 2 or more shots into one frame. Edwin Porter used this technique as well for the film 'The great train robbery' for the scene with the train going past the window and the scenery going past the door in another scene. At this time, it was technically impossible to do it at, for example, and actual train station because it needed a lot of light which wasn't around.

3) This clip shows a good example of green screening being used. Skipping to 27 seconds, it shows a part from 'Ugly Betty' where she is trying to avoid a news reporter and walks straight into a bus shelter which was unconvincingly filmed using green screen. The reasons behind it being filmed with green screen is because of various reasons such as, it's a lot less hassle, this is because if they were to use a proper public place then they would have to corner off the area to film it which would have to go by lots of people to do so and would need police around, as well they wouldn't have any control of ambient sound, so there would be lots of background noise which they could do without. This is why it's easier to use a green screen where you can edit in what you want and what sounds you want. This piece is very convincing due to the high level of technology clearly used as it looks like it's been filmed in a proper place.