Fixing Lighting Mistakes Bad Screen LightingĮnsuring good chroma screen lighting can mean the difference between hours of rotoscoping and an easy key. Yes, the compositor can fix that blue chroma screen with people wearing assorted shades of blue clothing in front of it with tons of rain and fog and bad lighting, but this takes time which costs money, usually lots more money than if it were fixed on the set. When encountering chroma screen issues on the set, this is the furthest thing from the truth. The Fix It In Post MentalityĪ huge error that many filmmakers make is thinking that it is cheaper and easier to fix all production problems in post. As a result of this, green, which according to color theory is the opposite of red, has become a very popular color for chroma screens.
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The color is too close to red, which is a major component of human skin tones. This is part of the reason why magenta screens are not heavily used. As you work with chroma screens, you'll find other exceptions such as not shooting an actor with golden blond hair against a green screen because the golden color is susceptible to bleed as a result of the colors being too close to each other on the color wheel. If everyone’s wardrobe is blue, you wouldn’t want to use a blue screen. Like everything, there are some minor exceptions to this rule. Typically, green screens are for shooting in the studios, blue screens for shooting outside, and magenta for covering objects that need to be placed into a green field bordering a blue sky. The Right Screen: Blue, Green or Magenta?Ĭhoosing the right color for your chroma screen for your shoot can mean the difference between rotoing a field of grass (if you put a green screen outside on a lawn, for example) or getting a perfect comp. Rotoscoping is often a last resort if a key isn’t working because it is a very time consuming process. Roto mattes are usually animated, often frame by frame. The process of rotoscoping (roto) is when you remove an object by drawing a matte around it. Mattes can be used to remove or isolate anything, and their shape, size and position can be fixed or animated. Often when keying, you’ll need to use a matte to prevent an area from being affected by a chroma key. You may also want to save it as uncompressed or with lossless compression to preserve your image quality and to make your compositing easier.Ī huge error that many filmmakers make is thinking that it is cheaper and easier to fix all production problems in post. 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.
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