A video file that is RGB + Alpha will save your color and alpha channels. If you key a shot and want to save it for later, you need to use a file format that supports alpha channels so the transparency information is not lost. This transparent area is referred to as an alpha channel. When a key is pulled, the green area of the shot becomes transparent. This is why it is important to control exactly how much green you are keying out so you don’t remove parts of the image you want to keep while removing the green screen. In other words when you key out a green screen, you are inherently getting rid of everything that is that color green in a shot. When you chroma key, the computer program takes all of a singular color or luminance value and removes it. Before we get into some common lighting problems, let’s take a look at how chroma keying actually works.

Compositing is a multi-step process that often starts with a key or a rotoscope. It is a process that employs multiple skills including keying, color correction, rotoscoping, matting an object and lighting correction. Compositing includes adding things to shots, removing things from shots and painting things out from shots in addition to bringing shots together. Typically, compositing is the art of taking multiple images that were not captured together and blending the assets to make them look like they are one singular image. Keying is a compositing technique, but it’s not the only one. We'll also examine some common visual effects (VFX) techniques that can be used to fix bad chroma shots. We'll look at some common problems and see how you can fix them while you're shooting.

Camtasia chroma key