Decide the size of your shot and how big your blue or green screen should be. When using a blue screen, avoid using clothes, props and sets with any blue shade. When using a green screen, avoid using clothes, props and sets with any blue shade. Ideally, a chroma screen should be large enough to cover the actor and all other elements seen on the frame. If shooting the actor in a long or panoramic shot, this requires a larger chroma screen, which may be the size of a large movie studio wall or even larger. If shooting only a medium shot of an actor around a space background, you may use as small as a12- by 12-foot chroma screen.
Create the space film effect to replace your green or blue background. Some create an entirely computer-generated image (CGI). Some create actual space shots for the process. Some combine CGI work and mechanical effects shot during the shoot or they combine CGI work and actual space shots for the space background the film needs. Depending on the kind of shots you need for the film, these can be a still or moving image of a space film effect.
Shoot the actor, props and sets in front of a green or blue background. All of them should be at least 6 feet away from the background. Also, make sure your background is evenly lit in order to avoid any problem with the quality of the replacement footage. Meanwhile, the challenge in shooting the elements around the chroma screen is that their lighting should match the lighting design of the space film effect. This is to ensure that the final film footage doesn't look fake on screen.
Transfer the footage into the hard drive to be used for the video editing.
Import the space film effect's still or moving image into the video-editing software, then drag it to the "Video Track 1" of your work area's "Timeline."
Import the chroma footage on a video-editing software, then drag it to the "Video Track 2" of your work area's "Timeline."
Temporarily turn off your "Video Track 1" or make it temporarily invisible so you can view the content of "Track 2" from your "Viewing Monitor."
Crop or garbage matte out the chroma footage by removing as much of the surrounding blue or green background as possible. This is usually found under "Effects," "Filters" and "Matte" options in your program's menu. Button names to be used depend on the video-editing program used.
Add the filters to make a chroma key by either using the "Chroma Smoothing" and the "Chroma Keyer" function. Load the clip with the chroma background into your viewing monitor, then go to the "Effects," "Filters," "Key," and "Chroma Keyer" options in your menu.
Remove the prior chroma background by using the "Eyedropper" tool. Select the portion of the blue or green screen near the subject, then use the "Select Color Eyedropper" tool to completely remove the green or blue colors on the footage. Fine tune the matte to make sure that no unwanted green or blue background is left out. Make sure there is no spill showing around the edges of your image's contours.
Turn on your "Video Track 1" or make it visible so you can view the contents of both tracks together. Use your program's image enhancement tools to adjust the colors and quality of the foreground and match it with the new background, which is actually the space film effect foootage on "Track 2." In certain shots, you may also need to adjust the overall quality of the space background or even blur it to provide better perspective to the shot's main subject. This gives the illusion of depth in your final composited image. Compositing refers to the combination of at least two different footage into a single footage.