Grass Valley Imagestore 750 v.3.0.1 - Manual (Page 56)

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Features
Keying Graphics
Linear keying is where the fill signal has been pre-computed to match the key signal. In this
case, the fill has already been cut by its own key independently of the Imagestore 750. The
keyer computes (1 – key) and uses this to “cut a hole” in the background signal. The fill is
then simply added to this.
Fig. 4-6: Linear Keying (pre-cut Fill)
Full keying is where the fill signal must be multiplied by the key signal prior to being added
to the modified background signal. In this case, the fill has not already been cut by its key.
The keyer cuts a hole in the fill with the key values and cuts a hole in the background with
computed (1 – key) values. The cut fill and cut background are then added.
Full Keying
Fig. 4-7: (both Fill and Background cut by Key)
• Sense
Key inversion switches the key value with the (1 – key), thereby inverting the sense of the
key signal.
The Imagestore 750 supports normal and invert sense.
• Normal
A black key level causes the fill pixel to be fully transparent.
A white key level causes the fill pixel to be fully opaque.
Intermediate keying levels produce a pro rata transparency effect.
• Invert
This is the reverse of the normal sense.
A white key level causes the fill pixel to be fully transparent.
A black key level causes the fill pixel to be fully opaque.
Intermediate keying levels produce a pro rata transparency effect.
• Masking
The Imagestore 750 allows a rectangular masking area to be defined for each of the 4 keyers.
This mask applies to any signals received by the keyer; whether they are external fill and key
signals or the output from internal stores.
For internal images, the area range of the mask is determined by the width and height of the
image in pixels, and is limited by the selected video standard. To maintain correct YUV val-
ues, the pixel count increments by 2.
For external fill and key signals, the area range of the mask is limited by the selected video
standard. Here too, the pixel count increments by 2.
×
+
Background
(1–key)
Fill Program
×
+
Background
(1–key)
Program
× Background
key