GT–2 • Glossary of Terms Vision Operator's Manual (v12.0 MD)
Hue — The characteristic of a color signal that determines whether the color is red, yellow,
green, blue, purple, etc. (the three characteristics of a TV color signal are chrominance,
luminance, and hue). White, black, and gray are not considered hues.
Internal Key — The use of a primary input to produce a key effect.
Key — An effect produced by “cutting a hole” in the background video, then filling the hole with
video or matte from another source. Key source video cuts the hole, key fill video fills the hole.
The video signal used for cut and fill can come from the same, or separate, sources.
Key Fill — A video input which is timed to “fill the hole” provided by the key source video. An
example of key fill is the video output of a character generator.
Key Invert — An effect that reverses the polarity of the key source so that the holes in the
background are cut by dark areas of the key source instead of bright areas. The KEY INV button
selects this effect.
Key Mask — A keying technique in which a pattern is combined with the key source to block out
unwanted portions of the key source.
Key Source — The video signal which “cuts a hole” in the background video to make a key
effect possible. Also called “Key Video”. In practice, this signal controls when a video mixer
circuit will switch from background to key fill video.
Key Video — See Key Source.
Linear Keys — Linear keys make it possible to fully specify the transparency of a key from
opaque, through transparent, to fully off. The transparency is specified by the key signal (also
known as the “hole cutter” or “alpha channel”) that is associated with the key fill. A keyer
capable of a linear key converts the key signal voltage directly to the transparency effect on the
screen. The KEY MEM button allows the user to store the Clip and Gain settings required to
match the incoming key signal to your requirements.
Line Frequency — The number of horizontal scans per second. For 525 line 60 Hz systems, this
is approximately 15734 scans per second.
Luminance Key — An effect in which video from one source is replaced by video that exceeds a
set level in a second video source.
Mask — See Key Mask.
Matte — A solid color signal that is generated by the switcher and can be adjusted for hue,
saturation, and luminance levels.
Matte Key — A key effect in which the fill video is a matte, provided by one of the internal
matte generators.
Memory — The memory feature provides storage and recall of complete switcher setups.
MIX — See Dissolve.
MLE — An abbreviation for multi-level effects.
PGM Output — The on-air video output of the system.
Primary Input — Video sources selected by the control panel push-buttons for the crosspoint
buses. These buses are normally labelled “KEY”, “PGM”, and “PST”.
PV Output — A switcher output that shows the scene that will go on-air when the next automatic
or manual transition takes place.
Self Key — A key effect in which the same video signal serves as both the key signal and key fill.
Soft Edge — A pattern edge effect produced by mixing key source and key fill signals in such a
way that the edge of the pattern is not sharp.
Split Screen — An effect in which a wipe pattern provides the key source signal. This is known
as a “preset pattern” key.
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