Help getting rid of black from Lens Flare Generator

Thanks for the info, I suppose I should've known this beforehand but there isn't enough time to do this to ALL of the lens flares that have been created for this project, which is a compilation of multiple motion projects (I'm referring to the final cut option that is) with many layers/sub layers. I guess the Luma key is the only chance...

I'm just a little confused as to why they would create a lens flare generator, or anything for that matter, that produces black or any other information in a space where you intend for there to be nothing? Clearly, if someone is using a lens flare wouldn't it be a defacto assumption that the area around it should be transparent, no matter what the blend mode, alpha, yada yada? Why so much extra work?

Also:

"That's because blend modes don't use alpha channels. Clips with blend modes applied use the info in the clips below them to determine transparency. As a result, any lens flare that you render out will have black on it."

- Does that mean there may be a way to keep the clip from using blend modes somehow so that it WILL use the alpha channel? Sounds far fetched but figured it was worth asking...

Thanks for your help!

Apologies - and one last question. If the blend modes to communicate with the alpha channel, what function are the other posts here on this topic addressing? They instruct to mess with the blend mode settings and seem to prove successful for those users, so I don't understand why that could provide a answer if messing with the blend mode doesn't actually affect the transparency?

Thanks, Andy, for the clarity. A lot of my questions probably stem from the fact that I am learning Motion, and all digital graphics, via tinkering and immersion as opposed to grammar school, if that makes sense.

For the record, I'm building a 2D skyline with transitions on each building as it turns from day to night, and all of the lighting on each (probably 40+ on top of actual real-life skyline footage) was constructed in Motion because I enjoyed the simplicity of the program and the amount of control without getting too detailed.

The only hiccup was making an aesthetic choice, in a sense, but also a logistical one, to render each building out as its own video (since they were made as separate motion files) with any fading/opacity changes (that are timed according to the length of the sunset) and then add each separate video into a master motion file, which has the already alive skyline as a base layer, and these building videos would each be in a group that I could then apply master changes to as well if necessary, such as color correction keyframes, etc.

I wanted to explain that because I'm curious if there's a way to do the FCP option, like, have the base city image and then put the individual buildings over that video track.

Nonetheless, I can understand why it might be assumed that lens flares would always be added over video in one file, but in my example, the shapes of the buildings with their lens flares allows for these flares to actually extend away from the boundaries of the buildings, as if they were blinking lights on spires, etc., so there are areas where it is just light/flare but nothing underneath. The point of layering these into another file was to minimize the processing demands of my machine, because I anticipated the motion file might be a bit heavy with SO many layers of blinking lights and buildings, etc., as opposed to just putting self-contained video files and doing more of a compositing job vs. 50 motion projects in one, but I guess that's another issue.

In my case as described then, it would be helpful to have the flares clear so that each video could be without the un-needed black, so that's why I figured that could be an option. Would you say the black would disappear if I imported the video into another Motion project file?

Message was edited by: JohnnyNeon

Between stumbling through this myself and stumbling into some other forum posts here, for other reasons, I found you on a lot and you've commented on questions about layering and transparency and equivalents to AE precomps, etc.

I read yours about making the clone layer, I wonder if that is a simple solution to what I am trying to do. Then I could "pre-render" each building (by having all of its elements in one group and cloning it out/importing it back in) and they would presumably have the flares and all, but with no unnecessary black?

Anyway, I'm trying it... if it is finished and working before you respond, thanks!