If you apply a color correction or lut to a track, it also affects transitions which, as you know, are not always at 100% of the video. It is trying to color correct the fades which are basically fades to black allowing the other track to appear underneath. You can see this by adding your LUT to a track and then change the transparency of the track. It will cause the color to shift or change in an undesirable way.

Yes, but it's getting the compositing math all wrong. There's no explanation for that erratic behaviour of the histogram as you drag through the fade, and especially at the bottom of the ramp, where the transparency is almost zero. If you change the transparency of the top track to 0, the LUT filter is still having a big effect. It shouldn't have any effect.

Thanks for looking into it. I meant to say the problem is there whether or not GPU is used, I have edited the OP.

Nick Hope, but then to verify, if you add it to the media in the media pool, then it works as expected. This does not surprise. It is adding color curves not to the media when it is on a track, but to the Track elements.

can we ANIMATE a reduction in the plugin at the fadeout?

First things first... I've been told that the Vegas LUT FX has no connection with the Vision Color plugin.

Nick Hope, but then to verify, if you add it to the media in the media pool, then it works as expected. This does not surprise. It is adding color curves not to the media when it is on a track, but to the Track elements.

Yes, it works as expected when used as a media FX. It is only as a track FX where I still think it is not behaving correctly. If you apply any other FX as a track FX, it will have no effect when an event on that track has zero opacity. For example a Color Curves FX which does very roughly the same sort of thing as that LUT (and in particular does not drop to 0 on the Y axis at the left end):

In that case, the effect of the FX falls gracefully to nothing when the opacity drops to zero. But the LUT Filter does have an effect at zero opacity.

Maybe this is just the nature of LUTs and inescapable. In any case I think it's good advice not to use the LUT Filter as a Track FX where you are using event fades or reducing opacity. Better to use it as a Media FX or Event FX.

can we ANIMATE a reduction in the plugin at the fadeout?

Probably, but easier to use the plugin as a Media or Event FX.

I had some contact from one of the Magix team about this issue. Easier to quote than try to paraphrase it:

"You bring up a slightly different point regarding correct application of alpha (opacity). I took a little time to recheck how this is being done and verify that the problem is with LUT Filter, not with its use as a Track FX vs. Event FX. As I mentioned earlier you'll see the same behavior when LUT Filter is used as an Event FX, if LUT Filter follows some other effect in the effect-chain which alters the event's alpha. For example, Chroma Keyer followed by LUT FIlter, or Levels followed by LUT Filter. In each of these situations LUT Filter does not reapply alpha after the LUT adjustment. This effectively allows certain LUT files, such as "SmallHD_MovieLook_ApocalypseThisVeryMoment.cube", to override the event's alpha and set the event's color to a non-zero value.

I'll add an issue to our bug tracking system to fix this so LUT Filter will correctly preserve the event's alpha."

I'll add this to the Known Issues thread as "LUT Filter FX does not reapply alpha after LUT adjustment", with a link back to here.

Edit: There was more discussion on this bug starting here: https://www.vegascreativesoftware.info/us/forum/3dlut-creator-pro-incredible-colometry-results-in-vegas-pro--111310/#ca687813

We do indeed have a fix for this and it will be available in a future update to VEGAS Pro 15.