Chromakey: Removing Background & Green Screen vs Blue Screen

by Joost | Last Updated: June 26, 2022
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Special effects are increasingly being used in films, series and short productions. In addition to striking digital effects, it is precisely the subtle applications that are increasingly used, such as Chromakey.

This is the method of replacing the background (and sometimes other parts) of the image with another image.

This can range from a person in the studio suddenly standing in front of a pyramid in Egypt, to a grand space battle on a distant planet.

Chroma Key: Removing Background & Green Screen vs Blue Screen

What is Chromakey?

Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range).

The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries.

A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in video production and post-production.

Playmobil petting zoo stop motion
Playmobil petting zoo stop motion

This technique is also referred to as color keying, color-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen.

Chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors.

No part of the subject being filmed or photographed may duplicate a color used in the background.

The first choice you have to make as a filmmaker is Green Screen or Blue Screen.

What are the strengths of each color, and which method best suits your production?

Both blue and green are colors that do not occur in the skin, so they are ideally suited for people.

When choosing clothes and other objects in the picture, you have to pay attention that the chroma key color is not used.

Chroma Key Blue Screen

This is the traditional chroma key color. The color does not show up in the skin and gives little “color spill” with which you can make a clean and tight key.

In scenes in the evening, any mistakes often disappear against the bluish background, which can also be an advantage.

Chromakey Green Screen

The green background has become more and more popular over the years, partly due to the rise of video. White light consists for 2/3 of green light and can therefore be processed very well by image chips in digital cameras.

Due to the brightness, there is a greater chance of “color spill”, this is best prevented by keeping the subjects as far from the green screen as possible.

And if your cast wears blue jeans, the choice is quickly made…

Regardless of which method you use, an even lighting without shadows is of great importance. The color should be as even as possible, and the material should not be shiny or wrinkled too much.

A large distance with a limited depth of field will partly dissolve visible wrinkles and fluff.

Use good chromakey software such as Primatte or Keylight, keyers in video editing software (check out these options) often leave something to be desired.

Even if you don’t make big action movies, you can get started with chromakey. It can be a cost-effective technique, provided it is used cleverly and does not disturb the viewer.

See also: 5 Tips for Filming with a Green Screen