by Sherri Sheridan
Using bluescreen special FX in your film will make it stand out more if you have a good reason to do it, and a solid story idea behind it to justify the wow shot productions. Bluescreening allows you to play with scale, location, physics, body parts, impossible stunts and character design collages in new ways. You could create huge monsters walking over little cities or live actors doing Kung Fu in a Barbie Dream House toy house. A dog head can be placed on a motorcycle racer’s body to create a new superhero fast. Characters could fly through the air, leap over buildings, ride skateboard down freeways, disappear in a flash, camp on the surface of Mars or walk around the inside of an atom. Bluescreen characters can be duplicated into an army, fall down bottomless pits, ride a flying chicken over New York or have their faces placed on objects that start talking.
Using Bluescreened Characters
Bluescreened characters are shot against a blue (or green) background, which is then made transparent in post using color filters. Other layers of video, animation or still images are dropped in behind, and around the characters, to create new environments. Actors are the most common subjects placed on bluescreens, but these same techniques could be used for stop motion sets or any time you want isolate a subject from a background as a layer. After Effects is the preferred software for keying bluescreen characters. The more expensive production bundle version has more features that make keying bluescreen characters much easier, along with several third party plug ins. You can also use simple color difference techniques to pull a character off of a background, if that is all you have available. What new narrative approaches could you invent to utilize bluescreen ideas for plot, character or theme?
How to Pull a Bluescreen
Everyone who does lots of bluescreening will have their own favorite presets of filter combinations to pull the blue color out and make a clean alpha channel in a program like After Effects. Each blue or greenscreen will be a slightly different color depending on the lighting, requiring different number settings sometimes. There are two basic approaches to pulling a bluescreen you may want to try. Lots of people say to use the Color Difference key first to pull the blue out, but I think you get a cleaner alpha channel using Color Range first. I then use the third party Puffin Composite Wizard (CW) effects plugins for cleaning up the edges around the bluescreen after the standard Color Range filter. Spill Killer or Suppressor removes the blue tinged halo from around the edges of your subject. You can type the setting in for both ways below and see which combination works best for your bluescreen situation.
Creating Shadows for Bluescreen Characters
Once you key out the blue areas around your character, and place them in your background, duplicate the character layer and fill it with black. Use a 3D tilt effect to place the black silhouette at a shadow perspective angle that fits the lighting in the scene. Add a 10 pixel feather around the edges of the shadow and take the opacity down to 70% depending on how hard you want the shadow to look. The shadow will then appear to be walking with the character, since it’s the same alpha channel image, just slanted and filled with black. How could you have the shadows doing different activities then the characters casting them? Perhaps one character is walking peacefully behind another, with shadows that are fighting to develop visually how they feel about each other. You would to do separate bluescreen shots for animated shadows to use this idea.
Bluescreen Shooting Tips
(1.) Carefully storyboard and time out each shot, to know which angle the character needs to be positioned, and for how long, to fit with the background footage layers.
(2.) Have the character pretend to react to things that will be composited later, such as screaming at approaching 3D monsters or holding their hands up right before a car is suppose to run then over in the final composited shot. If possible, use monitors on the set to key out the blue behind the actors, and drop in background layers, or digital set pieces. This will help you to see how well the actors are fitting in to your virtual sets as you shoot. Making bluescreen characters appear to really be in the final environment is an evolving art form.
(3.) For compositing one bluescreen character, actor, or pet onto another, try matching simple head turn motions for shots. If you are putting a human face on a cat, shoot the cat first. If the cat turns his head to the right after three seconds, have your bluescreen actor turn their head to the right after three seconds. In post you would place the face of the actor over the cat’s face. Ideally the heads would not be moving at all, but simple motions can be matched with a little planning.
(4.) Light so there are no shadows or hotspots from lights cast against your bluescreen. Your goal is to create a flat solid blue background behind the subject that make pulling a flat color key easy.
(5.) Avoid see through fabrics or reflective surfaces that will pick up the color blue and be hard to key out.
(6.) Avoid shiny objects on characters, such as mirrored sunglasses or chrome guitars that will pick up reflections of lights and blue floor.
(7.) Try to give yourself plenty of framing room between the bluescreen character and edge of the frame. If their hands or feet are out of the frame, it will limit your ability to composite them anywhere inside the frame as a full character. You can always take a fully framed bluescreen character and move them out of the frame a little.
(8.) You never want to scale any bluescreen footage up past 100% for good looking resolution. If you need a close up of a bluescreen character make sure and shoot for that size.
(9.) Turn your DV camera sideways for a maximum resolution when shooting full body bluescreened actors. If you shoot in regular landscape 4:3 mode, your bluescreen actor will be much smaller and lower resolution.
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