Green or blue screen backgrounds, also known as chromakey backgrounds, allow filmmakers and photographers to easily replace the background in a frame with almost any image or video. So, you can place your actors and models on a busy New York street, in a haunted house, or on the surface of the moon.
Both blue and bright green backgrounds are common in Hollywood, but what is the difference between the two colors and how do they work?
Where and how does chroma key work?
In post-production, chroma key makes it easy to replace backgrounds, use CGI and other visual effects. A solid blue or green background is digitally replaced with the desired photo or video.
It is often used in superhero, action and adventure films. So, for example, The Avengers was filmed on chroma key, and Johnny Depp in Pirates of the Caribbean.
However, the most common example of chromakey overlays are weather releases. In fact, the hosts are standing in front of a green screen in the studio, and all other images are superimposed during editing.
The most important thing to remember about chroma key technology is that its color will be digitally replaced on any subject in the frame.
For example, if the presenter is wearing a green dress in front of a green screen, her outfit will also be digitally processed in post-processing.
What to choose: blue or green screen?
Even though blue screens and green screens work in the same way, they are not completely interchangeable. There are certain situations where one color is more preferable than another.
The green used on the chroma key is slightly brighter than the blue. If you’re shooting night scenes, it’s best to choose a blue screen because there will be less light to bounce around and potentially cause problems when shooting. The extra brightness on green screens can be useful for daytime scenes.
Also, the green glow can lead to color blotches on some surfaces and textures, such as blonde hair.
When using any color on the screen, you need to pay attention to the color fringing around the edges of the object.
Many production designers prepare for this problem by using matte surfaces to prevent blues or greens from reflecting, and by preparing all sets, props, and costumes to avoid light reflections.
Blue screens usually cause fewer color patches than green screens. If you’re working on a green screen and often experience fringing, try blue chroma key.
Digital cameras vs. film cameras
If you’re shooting with a digital camera, in most cases it’s a good idea to use a green screen. The technology used in digital camera sensors is better suited for accurately capturing green. This is why most modern film productions use green screens.
Both blue and green are ideal colors to use in chroma key because they don’t show up in most human skin tones.
However, if the subject’s skin has a blue or green tint and you notice that you’re having problems with shadow color, fringing, or reflecting the subject’s skin tone, you might want to change the background color.
Sets, costumes, and other on-screen color sources
If you go to work knowing that you will be using chromakey technology, you should communicate your plans to the production designers from the very beginning. They will make sure that there are no bright shades of blue or green in the costumes, on the sets and props off the frame.
If you know in advance that the character should have a bright blue suit, use green chroma key and vice versa.
Output: green or blue screen
So we will use:
— blue screen when shooting night scenes; in the presence of a large number of objects that reflect light; if you have a hard time fighting with the green edging of objects in the frame.
— green screen when shooting daytime scenes when using a digital camera.
In addition, pay attention to the objects in the frame: if you have green objects in the frame, suits or, for example, the Hulk, use a blue background. And vice versa.
Folding chromakey: to be or not to be
Also, when choosing a chroma key, you may encounter another problem: choose a folding screen or a regular, fabric one.
Folding chroma key
Pros: does not wrinkle; easy to transport and move due to the folding design; you can do without a background installation system by leaning it against the wall.
Cons: it will not work to shoot a person in full growth.
So, for example, the foldable Raylab RF-12 on a flexible frame can be folded into a special case. Its size in the assembled state reaches only 50 cm. Moreover, it combines two colors at once — both blue and green from different sides!
Normal chroma key
Pros: you can shoot more complex actions, capture a person in full growth.
Cons: Wrinkles more easily, installation system required.
Raylab RL-BC01 — backdrop 3 meters long and wide. Made from muslin, it provides strength and durability to the fabric. The material absorbs light well and does not give glare. Don’t forget to purchase an installation system for it.
Thus, if you plan to shoot any objects or a person will be waist-deep in the frame, a folding background will be enough for you. For more complex shots, where you need to use a person in full growth, you will need a more difficult-to-use fabric chroma key.