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<< Camera Set Up | General Operations | Editing Systems >>
Chroma Keying
Chroma refers to color and key being the area of interest.
Chroma key is a technique for mixing two images together, in which a color from one image is made transparent, revealing another image behind it. This technique is also referred to as color keying, green screen, and blue screen.
It is commonly used by the weatherman on broadcast television, wherein the presenter appears to be standing in front of a large map, but in the studio it is actually a large green background. The meteorologist stands in front of a green screen, and then different weather maps are added on those parts in the image where the color is green. If the meteorologist himself wears green clothes, his clothes will be replaced with the background video. The color green is used for video because camera's are most sensitive to that color and is least like skin tone.
Prior to the introduction of digital compositing, the process was a complex and time consuming one known as "traveling matte". The blue screen and traveling matte method were developed in the 1930s at RKO Radio Pictures. The credit for development of the blue screen is given to Larry Butler, who won the Academy Award for Special Effects for The Thief of Bagdad (1940). The blue screen was used because of the sensitivity of the film used in the cameras.
The biggest challenge when setting up a chroma key background is even lighting and the avoidance of shadow, because it is best to have as narrow a color range as possible. The material being used affects the quality and ease of having it evenly lit. Materials which are shiny will be far less successful than those that are not. A matte surface will diffuse the reflected light and have a more even color range. In order to get the cleanest key from shooting green screen it is necessary to create a value difference between the subject and the chroma screen. In order to differentiate the subject and screen a two-stop difference can be used, either by making the chroma screen two stops higher than the subject or vice versa.
Software and Hardware
Serious Magic Ultra 2
ULTRA 2 is the tool digital video editors have been waiting for. It creates broadcast-quality backgrounds on Digital Video(DV), for convincing backgrounds with excellent results. Create 3D virtual sets and animated backgrounds -- enhance your productions whether they're corporate, educational settings, newsrooms or futuristic studios. Use it in the field or studio with minimal set up, for 3D virtual sets that are simple and affordable. Special effects, such as virtual camera fly-throughs, simulate realistic motion tracking within the scene Virtual Trak adds virtual pans and zooms from stationary camera shots, in perfect sync with your keyed backgrounds Flexible placement with edge cropping, scaling, and orientation settings allow total control over the placement of your source clips Real-time color correction on input and output clips along with spill suppression, color curve, and desaturation controls Video inputs for AVI, MPEG, Quick Time and DV files or any format with a codec installed Output files can be uncompressed AVI, DV, 24-bit, and 32-bit AVI's with alpha channel for later compositing with any standard video editing system.
Serious Magic $495
Datavideo DVK-100
Datavideo DVK-100 Chromakeyer - Y/C, Composite, 2 Camera Input, NTSC PAL
The Datavideo DVK-100 is a two camera live chroma keyer. It has many advanced features which can give excellent results even from less than perfect Chroma Key setups. This device features proc-amp adjustments, NTSC/PAL Capability and 3 types of keying.
BH $932
Reflecmedia Ultimatte
The Reflecmedia Ultimatte DV Chroma Key is a hardware based solution for Chroma Key applications. This keyer was designed to work with the DV video market utilizing Y/C, Composite and DV signals for foreground and background composited outputs.
BH $2995
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