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Video Chroma Key, Video Color Key, Color
Separation
Overlay, Green or Blue Screen, Background or Backdrop,
Video Compositing & Matting
- Model 617S
The Model 617S Video Chroma Key (Chromakey), Chroma Keyer, Video Color Key (keying) & Color Separation
Overlay system, is a two-input, one-output device that replaces a selected color in a "foreground" picture
with details from corresponding areas of "background" picture or backdrop. The video chroma-key removes the
selected color, chroma key blue screen (bluescreen), chroma-key green screen (greenscreen), for example, or a
narrow range of colors, from the foreground image to "reveal" the background image "behind" it.
This technique is also called video color keying, color key, chromakey green screen, chromakey blue screen, or
color separation overlay. Chromakey video can also be called compositing or matting, and involves adding a
different background electronically. A switch allows selection of the foreground image only, or the keyed image
consisting of elements from both foreground and background images. The Model 617S Video Chroma Key, Video Color
Key, and Color Separation Overlay system can also freeze the background or backdrop input so that it can continue
to be used for keying indefinitely.
In use, a key color is first captured by pressing the unit's "capture" button while the foreground camera is
viewing only the desired color. This color, for example, blue or green, can be subsequently checked by pressing
the "display" button. The unit's tolerance for error in the key color can be adjusted in terms of both phase and
brightness. For instance, the color phase range control could determine that only a very tight range of green is
acceptable for keying or that a wider range, possibly from blue through green to yellow is acceptable. Similarly,
the luma range control could determine that the key color is acceptable whether bright or dark, or could determine
that only a tight brightness range is to be keyed causing the unit to put in the background image where only
slight shadows are cast in the foreground.
Applications
TV Weather Forecast Map / Radar Image Chromakey Background
In the most common use of video chroma keying, chroma keyers, or a video chroma key system, a TV weather forecast
meterologist is placed in front of a green or blue screen as foreground and a weather map or radar image
is used as background. The chroma keyer removes the green screen or blue screen color from the foreground and
replaces it with details from corresponding areas of the background, causing the TV weather forecaster to appear
to be in front of a large weather map or radar image.
Movie Industry Video Compositing, Video Matting & Video Chromakey
Another common use of video compositing, video matting and video chromakey techniques is in the production of
modern films that integrate special effects with computer animations and backgrounds, live action video and
diverse locations.
Children's Museum Video Compositing, Video Matting & Video Chromakey
Some children's museums employ video compositing, video matting, and video chromakey systems to provide
instruction to their patrons in modern film making techniques.
Inserting Computer Generated Text and Graphics into Video
Colorado Video’s Model 617S Chroma Keyer can be used to add computer generated text and graphics to NTSC or PAL
Video. The computer should provide an NTSC composite video output. The text it creates should be on a uniform
background.
Connect the computer’s video output to the Model 617’s Foreground Video Input. Some computer video cards
sense whether or not the video output is connected at boot up. Therefore, this connection should be made before
turning on the computer. The Model 617 will not provide any useful video output without video present at this
input.
Connect your video source to the Model 617’s Background Video Input.
Connect a video monitor to the Model 617’s Video Output.
Connect the Model 617’s AC Adapter to power it up.
Set the Output switch to Keyed and the Background switch to Live.
If you’re computer is generating graphics on a black background, the Chroma Key may now be working. If not,
have the computer provide only the uniform background and press the Model 617’s Capture button for a second or
so.
Adjust the Range Set knob while holding down the Chroma button to achieve the best results. Then Adjust the
Range Set knob while holding down the Luma button to achieve the best results.
Flipping the Output switch to Foreground Only will display the computer graphics alone. Flipping the
Background switch to Freeze will freeze the Video at the Background Input.
Features
617S: Video Chroma Key, Video Color Key System
Replaces selected key color, like blue or green, in foreground picture with background picture
Phase and luminance ranges of key color are adjustable
Background picture can be frozen
Key color can be displayed for verification
Built-in frame synchronization- genlocked cameras are not required!
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PO Box 928 Boulder, CO 80306 USA Tel +1-303-530-9580 sales@colorado-video.com Fax +1-303-530-9569 www.colorado-video.com
Business Hours: 9AM to 4PM Mountain Time (GMT-7 Winter, GMT-6 Summer), excluding weekends & holidays.
Copyright 2004, 2008Colorado Video, Inc.
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