GRASS VALLEY 1200, Installation And Service

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Section 3 Ñ Functional Description
Transition Generators
The Transition Generator (Figure 3-16) creates the control signals for each
of the mixers.
The T1 and T2 (Transition Old and Transition New) are created by the Clip
and Gain from the Wipe Pattern. Pattern Old is the outer edge of the old
video. Pattern New is the inner edge of the new video. The space between
the two (if any) is the border. T1 and T2 go to all of the Transition
Generators where they are used to determine the location of the wipe.
To create a control signal for a particular video the Transition Generator
must have information on that layer and any layer above it. The Key 1
Transition Generator has inputs for the Key 1 and Key 2. If Key 1 is in front
of Key 2, the Key 2 input will be ignored. If Key 2 is over Key 1, the Key 1
Transition Generator will only output a signal where Key 2 is not hiding
Key 1. This is determined by the Priority Depth Signal.
There are two outputs from the Transition Generator: the Key 1 Transition
Signal and a Summation Output which has that Transition Signal and any
previous transition. So the Key 1 Summation is entered into the Key 2
Transition Generator and the Key 2 Summation is entered into the
Background A Transition Generator.
The Key 2 Transition Generator is identical to the Key 1 Transition
Generator except that the Key 1 Summation is entered into the Key 2
Transition Generator.
Background A is considered to be over Background B and both keys are
over both backgrounds. Considering this, the Background A Transition
Generator requires Background A, Key 2 and Key 1. The Background B
Transition Generator requires Background B, Background A, Key 2, and
Key 1 as inputs. Each of the transition controls goes to the appropriate
mixer.
Since the border transition will vary depending on which key is on top
there are two Border Transition Generators: one generator with Key 1 on
top and the other with Key 2 on top. The Border Mixer uses the Depth
Signal to determine which of the transition controls to send to the output.
The Key Summation also goes into both Border Transition Generators and
a mixer decides which of these should be the Clean Key output. The Clean
Key output is a composite of all keys except the DSK. If both backgrounds
and the border between the backgrounds are all black, then the Clean Key
is a composite key (less DSK).