How Does A Green Screen Work?
At Shoot Systems we utilise green screen technology in many of our innovative solutions such as photo booths and bullet time photography, but just how does a green screen work? It’s one of the most common questions our customers ask us once they’ve experienced our fantastic photo and video systems.
It’s magic! What else do you need to know?
With the first uses dating back to films in the 1930’s, green screen technology has developed throughout the years allowing the film industry to create movie magic and display just about anything you can dream of.
With the amazing effects that can be created, it’s easy to imagine the process is extremely complicated yet the principle of green screen is actually very simple:
- Take an image of something in front of a background with a constant uniform colour, which is generally a primary colour of green or blue.
- This image is then fed into a processing system that looks through every pixel – looking for a match to the colour range.
- Once a match is found, this is then removed and made transparent (the end result being very similar to that which goes into photo editing software – erasing all green or blue). It’s this erasing process that really makes a green screen work as it provides a blank canvas to add in backdrops.
- The transparent image is then superimposed in front of a background, so that the resultant image shows the subject and background as a single image.
The process is identical for both photos and video because a video is actually just a stream of still images at 25 – 30 frames per second. The green screen system has to analyse each frame and remove the required colour. Once the colour has been removed it will output a frame with transparency where the green or blue used to be.
Why green or blue?
A common question is why are those colours chosen for the screens and not any other colour? Simply, it is generally accepted that these are the furthest away from skin colours which makes them the best option.
When members of the general public are being filmed, green is preferred as people tend to wear blue more often. In a professional environment such as film and TV where there is much greater control over what people wear, blue is often used as it is softer and can be a closer match to the background image.
Can things ever go wrong?
Unfortunately that general rule doesn’t always run true! I recall a situation where Shoot Systems were providing a green screen service for a Santa setup and it turned out that in one region it was customary for families to all dress up as Elves. We ended up with a stream of green Elves to photograph leading to lots of floating heads on that day! That’s why we always try now to make sure our customers are wearing as little green as possible to help make our green screen work as effectively as it should.
Depending on the setup, green or blue outlines may appear around the edges of the subject. If the superimposed background is a weather forecast map for example, blue may well be chosen in order to make these outlines less noticeable (visa-versa for say a shot of a lawn or landscape).
How to prevent this happening
To avoid any outlining or fringing issues, care must be taken when considering what the subject is to be superimposed onto. For example, you do not want to green screen someone and superimpose them onto a white background as any problems with colour drop out or fringing will stand out like a sore thumb. Look for a background that is sympathetic to the colour being used.
Lighting is also major consideration in ensuring a great image. If there is a dark shadow on the background that is cast from the subject, this will create a dark area that will not appear as green or blue to the processing system. This can result in areas of the image not having background removed and can certainly spoil an image! To combat this issues, use lighting that is at an equal distance and angle from the subject to cancel out shadows. You will also need to keep the subject away from the background so that any shadows on the background are soft enough not to cause a problem.
Now that we’ve answered the question ‘how does a green screen work?’ you can see that whilst the technology is simple enough, in theory there are so many things to take into consideration to achieve a flawless result.
With many years’ experience and a real passion for what we do, the team at Shoot Systems apply our expertise to all of our bespoke photo marketing solutions to create immersive and stunning visual effects. Feel free to contact us for more information!