[v7 General Discussion] Upstream Keying

We have EW7 working with a Blackmagic ATEM TV Studio set up as described in

We are finding that when we overlay a video over a live camera feed using the premult setting on the ATEM there is a ghost of the Camera feed showing behind the Video. This can be overcome by either selecting the Easyworship feed as the background video in ATEM or by turning off the premult setting but both of these require coorsination between the ATEM changes and the Easyworship changes making it hard to achieve crisp transitions. The alternative of leaving premult off on the ATEM means that other items that we have designed to overlay with semi transparency do not achieve semi transparency (they are cut in at the point determined by the clip setting).

Does anyone know how to achieve semi-transparency whilst also having videos keyed in 100%? I think the issue is either that the EW7 Alpha channel is not 255 or if it is then the premult setting on the ATEM results in some mixing even though the alpha channel is 255.
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I have now run a further test with a powerpoint presentation with 2 slides one totally Black (0,0,0) one Totally White (255,255,255) played through EW7. Both slides when used in the Upstream key of the ATEM Television Studio with pre-multiplication setting end up with the background camera showing through. I think this proves that the Alpha channel from EW7 is not 255 but more like 200. So my question is can this be changed to make it 255?