Video and Key Signal Paths
1-29
1
Start Here
Index
Contents
The video for each channel is read out of the transform framestores, with
addresses generated by that channel's transform controller, and sent to the out-
put interpolators. The transformed video and generated key information from
each channel passes to the combiner, which composites the two channels
together.
The combining process uses either a fixed key priority (A over B or B over A) or
a Z (depth) based key priority. In Z key mode, the Z position of each channel
in 3D space determines its priority relative to the other channel. The graphics
output consists of axis grids and channel identifiers for each channel.
Video+Key Mode
The Video+Key mode differs from the Video+Video mode
only in that the board processes the B channel as the key signal for the A chan-
nel, with additional key clip, gain, and horizontal phase adjustments. Note that
the chrominance processing of the B channel is not used in this mode since key
signals have luminance information only. This makes the A channel 4:2:2 and
the B channel 4:0:0.
The A/B Combiner's key output is effectively that of the B channel, and not the
raster-based signal seen in the Video+Video mode. Since the key (B) transform
can be independent of the video (A) transform, it is possible to position the
transformed key so that the transformed video is not visible, or only partially
visible, in the final composited output.
