Chroma key: instructions for use | Lesson | Photo, video, optics

Chroma key is a green or blue background. In post-processing, it is easy to cut out, which allows you to change the backdrop to any other without the slightest difficulty and complement the frame with a new reality. This is a good way to save money on complex decorations. Films and series with a lot of special effects are shot on chromakeys, such as The Avengers or Game of Thrones, TV programs with weather forecasts and, of course, photos.

We tell you what chromakeys are and share the secrets of how to work with them.

Chroma key background — views

The main principle that a good chromakey must meet is to be as different from the subject as possible so that the main character can be easily cut out in processing. With this in mind, it will be easier to navigate the variety of choices. We tell you what chromakeys are and how they differ.

Chroma key color

1. Green chroma key.

The most common chromakey color. In most cases, this is a really universal option — human skin and hair are as different from green as possible, so the object is easy to cut out. This is especially important when shooting video, where they try to automate this process so as not to cut each frame manually. Another advantage is that less light is needed to illuminate the green color.

Green chroma key is not suitable if:

— the hero is dressed in green clothes, made up as a mermaid, an alien or Shrek with green skin;

— you shoot in the evening. For such situations, a calmer and darker blue color of the chroma key is suitable — it is this one that is used for filming at night or at dusk.

2. Blue chroma key.

When the technology of working with chroma key was just invented, it was filmed against a blue background. This went on for several decades — until about 1970, when green, a color that is more contrasting to a person and less common in clothes, gradually began to displace blue.

Blue chroma key is used in evening street photography, as well as in situations where the object is painted green.

3. Red and bright orange chromakeys.

Rarely seen. I only use them for subject photography. When the background is removed, the skin of people on such a chroma key will also be included in the selection and erased.

Chroma key material

1. Paper chroma key. One of the simplest and most budget options, which is most often found in photo studios.

Cons of paper chromakey:

— difficult to transport;

— small size. The width of a paper chromakey is usually only 2-3 meters. This is enough for subject shooting, or portrait, but a maximum of one person.

2. Fabric chroma key. There are both small backgrounds and large-scale seamless canvases for high-budget projects. It’s lightweight, easy to carry, and wraps around objects with no problem when you need to drape a furnished room or outdoor space. Fabric chromakey is also found in photo studios.

Cons of fabric chromakey:

• price. Especially if you need a large canvas;
• bruises and creases on the background. It is believed that the fabric chroma key does not wrinkle well, but the problem is still possible.

3. Non-woven chroma key. It is made from thread and fiber, which are combined using mechanical processing and exposure to temperatures. This makes the background seamless. In addition, it is lightweight and easy to carry.

Cons of non-woven chromakey:

• Harder to light properly, can make it harder to remove the background in post;
• The material is riddled with small holes (this is called perforation). Because of this, the hero needs to be placed farther from the background than on chromakeys made of other materials.

4. Chroma key cyclorama and chroma key paint. A section of the filming hall or the whole room, painted in one color. In photo studios there are black and white cycloramas. Green ones are a rarity and these are, as a rule, film sets of film studios. There are separate studios where the hall can be rented, but it is quite difficult to find them.

Cons of chroma key cycloramas and pavilions:

• rarely found;
• expensive rent.

Working with chromakey — 10 tips

• The most important thing in the work is light. The more evenly and more brightly the chroma key is during shooting, the easier it will be to remove the background.

• Get ready that you may need 4 or more light sources to work with chroma key.

• For background lighting, use the largest softbox or octobox available to you.

– Separately light the character and the background, which should be much brighter than the model.

– To further separate the model from the background, use a backlight.

— Think in advance about the color of makeup, makeup, clothes and accessories of the model. Depending on them, choose a contrasting chroma key background.

– Place the model away from the background so that shadows do not fall on the chroma key. A good distance is at least 3 meters.

• In addition, powder will help reduce green reflexes on the face, which will make the skin more matte.

• Choose the right chroma key width. If you shoot a model to the waist — 2 meters is enough. If you are photographing in full growth, then at least 3 meters. When there are two or more people in the frame, then expect that the width of the chroma key should be at least 5 meters.

• Choose spacious areas for shooting with chroma key — the background and lighting will take up a lot of space. In addition, the model also needs space to move around in the frame.