Grass Valley Switcher Products - Manual (Page 13)

Switcher Products — Protocols Manual13
Tally System
incoming key signal or a wipe pattern generator. The video input contrib-
utes to the key if it is used as either the fill or as the key source. The key
input contributes to the key if it is used as the key source.
An opacity setting of 0% negates all contributions of the keyer.
The processed cut signal or the masking signals may also change video con-
tribution. If the result of key processing produces a completely transparent
(i.e., cut signal is 0 for the entire raster), the video signal is not contributing
to the key output. This calculation is normally not considered since it
requires real time sampling of the cut signal and existing key processor
ASICs do not include the calculations.
All of these factors are combined into a single flag within the contribution
tally packet.
Transition Mixer Modifications
The transition mixers modify the contribution of all inputs to an ME bank.
If the mixer makes an input transparent, there is no contribution to the
mixer output for that input.
Separate contribution flags are provided for each path into a mixer. Each
mixer (the Kalypso system has four per ME, for example) has its own set of
contribution flags in the contribution tally packet.
Internal and External Processing Loops
Images processed by DVEs, frame stores or other devices must also receive
accurate tally. Since these devices have the ability to make their incoming
video invisible, their current state must be included in the switcher tally
calculations. For example, if the DVE positions an image completely off
screen or the frame store is frozen, the on-air tally for that source should go
away (assuming it isn’t on air via some other path).
Tally System
There are many inputs, outputs and paths through a production switcher.
The tally system must be capable of determining which sources contribute
to a specified output regardless of contributions to other outputs. In
essence, there may be multiple tally paths through the switcher just as there
are multiple video paths. It is essential to maintain tally independence back
though each video processing path of the switcher and external gear (e.g.,
DVE).