Essay, Research Paper: Blue Screren Compositing

Creating just the right effect can be difficult if not impossible without many of the tricks employed by today’s directors and special effects artists. Once the exclusive domain of Hollywood, blue screen imaging is fast becoming a readily accessible visual tool for today’s vidographer. It is hard to imagine movies like Jurassic Park without its dinosaurs or the Matrix without it’s impressive visual effects. But many effects like these could not be completed without effective blue screen techniques.
So what is blue screen? Creating a blue screen composite image starts with a subject that has been filmed or video taped in front of an evenly lit blue background. The blue screen process replaces the blue in the image with a previously filmed background image or plate.
Blue screen is sometimes known as chroma–key which refers to a television process. Ultimatte a manufacturer is also an exclusive process that produces a high quality blue screen image. Using Ultimatte it is possible to add subtle effects like mist or haze to an image using software like Photo Shop and Aftereffects.
Chroma-Key is a process where the video device, keyer focuses on the blue background and makes it transparent thus allowing you to create a composite image with your background image plate. Original keyers primarily used the blue channel of the video camera creating very jarring and unpredictable effects. Modern keyers however create very reliable and even composite images.
Blue is primarily used because flesh tone contains no natural blue tint so it just made sense to use a color that keyers could tell easily apart from the subject. Blue is also easier to use because in three camera set-ups such as the nightly news any cameras that are not hooked up to the keyer would easily see a bright green or red backdrop. It seems easier for set designers to make more believable sets that include a blue sky. Modern keyers are becoming substantially more sophisticated and can easily tell the difference in the hues. It is becoming more common to see the other two video colors red and green being used where the subject matter requires it.
Lighting is difficult with chroma-key and Ultimatte. Great care must be taken to make sure that the blue, red, or green backdrop is very evenly lit with no shadows or highlights basically flat. However the subject may be lit any way that you choose. Ultimatte keyers have very fine controls that allow for exacting adjustment of the way that the background image will be composited. This can sometimes make up for subtle defects or shadows in the blue screen.
A waveform monitor is standard equipment in a blue screen video shoot because it gives a graphical representation of video levels in a scene. Small inconsistencies in the video levels become very obvious when viewed through the waiveform monitor. A spot light meter will not give you the consistent results required for blue screen compositing.
So the next time you see people hanging off of a cliff in a commercial or watch your nightly news. You will have a greater understanding of just what it takes to accomplish such stunning visual illusions.



Bibliography


Producing a First-Class Video for Your Business
Dennison, D. Doman, D. and Doman, M. (1992). Producing a First-Class Video for Your Business: Work with Professionals or Do It Yourself. Vancouver BC: Self-Counsel Press.
Ultimatte
http://www.Ultimatte.com
BlueScreen LLC
http://www.bluescreen.com
Hollywood SFX
http://www.geocities.com/Hollywood/Makeup/9472/sfx.com
The Blue Screen Page
http://www.seanet.com/Users/bradford/bluscrn.html


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