At Onlea we use many cinematic techniques to help distill complex academic content into engaging, storified online learning tools. One of the key techniques we use is greenscreen filming. This allows us to have a presenter share the screen with data, images, graphs or any other imagery that helps us show and tell for the learner. Heck, we can even immerse our presenter into a black hole, or put them safely amongst a pack of velociraptors! Clever girl! One of our best animators is Suzy Spence; she has done animation for a number of great organizations including Warner Brothers & LG. Suzy, has kindly shared a little slice of her expertise with us. Here’s her step-by-step guide on how to properly Chroma Key a subject that has been filmed in front of a greenscreen.
When you see some of our Onlea productions, you can see the compositing of two images. I would like to introduce you to the Adobe After Effects’ Chroma Key tool which we use to easily composite two different images.
What is the Chroma Key?
Chroma Key compositing, or Chroma Keying, is a post production tool for compositing two images or video clips together based on color (i.e. greenscreen). But before we can use Chroma Key we need to shoot some footage against a greenscreen.
Tips for Shooting on a Greenscreen
- Avoid shadows or too much brightness.
- Light is very important in front of a greenscreen. It’s best to avoid shadow, which may be caused by putting objects or models too close to the greenscreen, or by uneven lighting. Also, try to avoid using extremely bright light as it may lighten the greenscreen too much.
Avoid green objects or wearing green clothes - even green eyes!
Set the camera to a high shutter speed in order to prevent motion blur in the video.
Let’s Take the Green Out!
In this section we will discuss using Adobe After Effects’ Chroma Key. You can use it in Adobe Premiere Pro as well but After Effects’ Chroma Key has a more detailed functions.
- Import your video clip and create a new composition.
- Colour grading the clip before Chroma Keying helps make a cleaner video image. (Effects > Lumetri Colour)
- Use the Effects & Preset > Keying > Keylight (2.0)
- Change Options (This is an essential step)
Screen Colour (b): Pick the middle of the greenscreen and extract the green colour.
- Change View (a): Alternatively keep checking between Screen Matte and Final Result.
- Screen Gain (c) / Screen Balance (d) and Screen Matte > Clip Black (e) / Clip White (f): Find the best Chroma Key setting for your video by adjusting those four sections. Try to make the object pure white and the background pure black in the Screen Matte view.
- Focus on the edge of the object.
Sometimes we need to make special efforts with the edges of our objects because they may not look natural if the object is blurred due to its motion or if the object has an intricate/fuzzy edges (e.g. hair). In this case, we have to make further adjustments to our Keylight 2.0 settings.
Extra options for detail in Keylight 2.0
- Screen Rollback: This option makes the object’s edge come further inside
- Screen Softness: This option makes an object’s edge soft
- Replace Colour (g): Choose a similar background colour that will be composited with the object
- Hard Colour or Soft Colour (h): Choose the best option depending on your images
Now you can composite your two video images easily using Chroma Keying!