Using Genlock, Overlay, and Mix
Probably the r eason why you bought the Eclipse was to use t hese featur es, so this section
is dedicated to describing these in more details.
Basic functional diagram of the overla y circuit
Mixer
Scan converter
and Genlock
Keyer
Vi de o input
Video
Out
Video
Key
PC In
RGB
Out
The above diagram gives an idea of how the unit's overlay circuit functions.
Video (either composite or S-video) is fed into the un it, and the Scan Converter circuitry
is 'locked' onto this. The Scan Converter output is fed t o the Video Mixer, where it is
mixed accordingly to the Key signal from the Keyer circuit.
Note that the RGB Output does not pass through the Video Mixer and hence cannot
support overlay features.
Advantages of this circuit
A different method of overlaying is to fully decode the incoming video signal into
separate components (RGB or YUV), m ix t his with the scan converter components, and
re-encode back to video. The Eclipse's method provides several advantages over this
method:
The video input signal is never decoded, so remains at a very high bandwidth -
especially true when using a composite video input.
Signal delays (from video input to output) are minimized to approximately 20ns.
Sync pulse widths and subcarrier frequency of the video input remain unchanged.
Video input sync & subcarrier SC/H timings are unaffected.
Keyer circuit
The exact m ethod that the Keyer genera tes th e Key si gnal depends on th e overlay mode
being used (Genlock, Overlay, Mix), and other signals such as Keyer (V.Soft / Soft /
Normal / Hard), Key Level, and whether the computer overlay portion is faded or not.
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