Bluescreen Studio – Technique and Application Examples
With a bluescreen you can place an actor in any environment. The blue of the bluescreen studio is replaced by a movie or a computer animation.
What to consider when building the blue screen and the implementation of scenes will be answered here.
If filming a scene for real would be to dangerous, it can be seperated in two parts. If for example Bruce Willis have to run between two moving trains. For the background a camera is mounted between two railway tracks. For the foreground Bruce Willis is filmed in a bluescreen studio. Then he is blown by a fan and the studio has a lighting situation that fits the background. After the bluescreen background is replaced it looks like Bruce Willis would run between two moving trains, as you can see it in „Mercury Rising“.
Mercury Puzzle (1998): IMDB Mercury Rising
The scene sould be carefully planned and visualized using a storyboard. How should the person stand, how should he move? The new background whether filmed or created in the computer should already be filmed or at least visualized. The more accurate the scenes were planned, the easier the orientation in the virtual space will get. With this you can also avoid continuity problems in post.
An even illumination with area lights ensures a homogenous background. Bright spots on the background have to be avoided because the light cones of those spots are overexposuring the blue color. The background is getting white so that it cannont be keyed by the bluescreen-keyer. You need a blue which is as perfect as possible. The color of your light source can affect the color of the background positively and negatively. Fluorescent tube are avaiable in different color temperatures. 3200K is reddish tungsten light, 5500K is bluish daylight. When using spotlights the color can be changed using color filters. In practice you have to test what works best for you.
As background you can use, blue fabric or background paper or the color is painted directly onto the wall. Fabrics have the disadvantage that the color is usually not exactly equivalent to an RGB blue and the material absorbs a lot of light. Wrinkles in the fabric also worsen the keying. Background papers have no wrinkles, but when someone walks on the bluescreen, it can tear very easy. Special bluescreen wall paint contains reflective pigments, achieving a smoother and brighter surface but it’s more expensive. However even then the blue spill, i.e. the reflection of blue light on the actor, which is bad for the keying, is bigger.
The technique is the same. What’s important is the clothing of the actors whether to use a greenscreen or bluescreen. The camera technique also makes a difference. Most consumer cameras have a chroma subsampling. A part of the compression is achieved by reducing the color resolution. The human eye has more sensitivity for the luminance resolution. The lightness and therefore the sharpness is mainly determined by green. With digital cameras a greenscreen can achieve better results if the clothing or the product allows it. A green machine cannot be filmed in a greenscreen.
This is relatively easy. You put a desk in the bluescreen. An actress sits behind the desk on the right side of the picture. On the left you can show graphics or videos. For bluescreen keying you can use Adobe Premiere Pro for example. Professional actors are able to speak the text fluently from memory. For amateurs, if memorizing does not work quite as good, a teleprompter can be used, which they have on television, or large text cards. For the sound you can use a wireless lavalier microphone on her blouse/his jacket or a boompole.
The largest problem is an even illumination of the bluescreen/greenscreen. Its color should be as close as possible to 100% blue/green. The actors clothing have to be as far away from this color. The imagination of the actors is as important as the right instructions of the director. Storyboard drawings, prints of the 3D background and eyeline markings in the studio can help the actors to imagine the scene even better.
Here’s an example for the possible applications of a bluescreen or greenscreen in a music video. The video seams to be filmed in one single camera shot. The scene in the music video is consits of several camera shots which are keyed and then positioned in 3D space and then composed to a single shot. The white dots on the bluescreen are tracking points. They can be used to reconstruct the camera movements. A virtual camera in a 3d render software can thereby follow every camera move. The camera can be moved freely in the bluescreen studio while the background follows this movement exactly. The recording was done uncompressed using the HD-SDI connection of a Canon XLH1 in progressiv mode to avoid color subsampling.
In a bluescreen or greenscreen the most important thing is an even illumination. We made the best experiences with cold fluorescent tubes (5000-6000K color temperature). In the production of a film in a bluescreen a good planning is crusial so that everybody on set has a similar picture of the final scene in mind.
Here’s a side-by-side bluescreen video: bluescreen studio of the UNEM-Filmproduktion
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