Prerequisites of a Good Keying

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Introduction

While preparing for green screen production by far the most important thing is to properly prepare the background. If the background is not well prepared you cannot have a perfect result, even if the keying process in the software is done properly.
This article lists all the necessary elements of preparing the background before production.

Preparing the Background

Depending on the material used as background, there are different issues to look out for, but in general, these are the following:

• Check if the background has any visible imperfections and fix them if it has.
• Avoid creases in the material.
• The background should not have any holes, tears, or ruptures.
• Make sure the background is clean and that there are no dirt spots on it.
• The background should disperse the light as much as possible and have no reflections or shiny parts

Preparing the Lighting

To achieve a clean result, good lighting is a must. When using clean plates, the uniformity of the background is not as important, but it shouldn't change during production.

Background Lights

The aim of the background studio lights is to light the green background as evenly as possible. Generally speaking, the more even the background is lit, the clearer the final keying will be. Illumination of both the talent and the background should be homogeneous and major casted shadows on the background with high contrast should be avoided.

You could also aim to use real shadows in your final composite. In order to make it look natural you need to be mindful of some things:

• The real-life shadow should align with the light sources in the scene
• The shadow only should be cast to the floor, and not to the back or side walls

Talent Lights

When you are setting up the lighting for your presenter (with the talent lights), you should keep in mind how it would affect the lighting of the background. Moving or talent-tracking spotlights is considered a bad idea since in most green screen setups they would ruin the balance of the background lighting.

You should also consider matching the lights of the virtual studio to the real studio, so the talent will look more like part of the virtual scene. This way you can achieve more realistic virtual setups.
Think about the environment in which you are composing your subject. However, the green and talent should always be well-lit. If the talent should be darker in the composite then change its brightness in Aximmetry

Example of a Bad Lighting Setup

As you can see in the image below, the lighting of the background is far from even. The left side is way more bright than the right side of the Green Screen.

Example of a Good Lighting Setup

Camera Settings

We strongly recommend turning off auto exposure in your camera.

It may seem counterintuitive, but when shooting a green screen, you want to saturate the screen—in other words, darker is better. There are a few reasons for this. One is that a well-saturated screen provides good color separation, while a bright screen can be harder to key. The rule of thumb is to have your screen be ¾ of a stop darker than your key light. In addition to pulling a better key, a darker screen will project less reflection, also known as spill, onto your subject. This spill can contaminate your foreground subject, making it more difficult to pull a matte/key with clean edges.

Preparing the Objects and the Talent

Dressing the talent in colors that show high contrast is preferable. High contrast helps the software to differentiate between the talent and the background. Green (or the color of the background) and colors that can reflect green, should not be worn.  Reflective accessories, such as jewelry, tend to be a bad idea. They reflect a high amount of green, which leads to holes in the final image.

The same idea can be applied to objects, such as chairs, tables, or bottles. Green objects will be cut out with the background, and reflective parts (like chrome-plated legs) can result in holes in the final composite.

Positioning the Talent and Objects of Interest

You want to keep your subject as far away from the screen as possible. This way, the talent can be better lit without the lights affecting the background, and the distance also keeps the reflection of the green background of the talent, which will result in better keying.

Continue to Keying

Once you finished preparing your Green Screen, you can move on to the Keying:

Keying