Blackmagicdesign ATEM Mini Installation And Operation Manual page 53

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Your TGA file is saved.
Now you can open ATEM Software Control and load the file into the media pool.
From there, drop the graphic into the media player and the alpha channel you saved
will automatically be loaded into the media player key source. The key source uses
the greyscale image in the alpha channel to tell the linear keyer transparency values
for the graphic.
If you switch the linear key to air, you will now see the graphic keyed over the
background with perfect transparency.
ATEM Software Control 53