Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC[2]), or by various terms for specific color-related variants such as green screen, and blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate a color used in the background.
Here are important guidelines to follow.
• Contrast the color of the background screen & subject
• Be careful of white, black, gray
• Avoid red, yellow, brown
• Use a saturated color if possible
Contrast the color of the background screen & subject
This is a very important rule! The color used for your backing screen should NOT be present in the subject. If your model is wearing a blue shirt and she is photographed against a blue backing screen, the shirt may visually disappear when the blue background is removed.
Be careful of white, black, gray
Some photographers try to solve the issue of color spill by using a neutral background of black, white or gray. While this cuts down on lights reflecting color onto your subject, it may cause other issues.
Black, white and gray baking screens are often problematic because those colors are found in almost every foreground object. Shadows are mostly composed of black. Highlights almost always contain white. A value of gray is often lurking in another color. This makes pulling a key extremely difficult, since Primatte doesn't know what color to focus on for extraction.
Avoid red, yellow, brown
Another color that you need to be careful of is red. A red screen can get too entangled with the red skin tones of human models. This is also true for yellow and brown since they are almost always found in skin tones. Blue and green are the best choices for photographing humans because these colors are least likely to be found in skin tones.
Use saturated color if possible
If possible, use a saturated color for your screen. For instance, a rich blue will always work better than light blue or turquoise. There are numerous screen products manufactured in the colors of 'Chromakey Blue' and 'Chromakey Green'.
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