Rendering/Compositing - Can't get a transparent background in my render

I’ve been using Blender for about a year now so I’m familiar with most of the functions. I have spent most of my time rendering images with transparent backgrounds, but I’m experiencing a really odd problem with my current project: for some reason, Blender’s adding a black background to my renders.

This could be due to composition, but I put it in this category because it could be one of the other.

I am using Blender Render.

I know the basics of setting the export image type to .PNG, selecting RGBA, and setting the Shading Alpha to “Transparent”. When I started experiencing problems I unchecked “sky” from the “include” sub-section in the Layers section. This may be important but perhaps not.

In the compositor, I checked all of the preview windows for my render layers inputs, and all of the backgrounds are transparent. Even if I trace everything to the last step prior to “pluging” it into the composite node, the background is still transparent, yet the output yields a solid black background… I am really confused!!!

One last detail that I think might help - another issue - is when I add stars. When I do, Blender adds then onto a transparent background (so it only renders the stars), and then for some reason in compositing places them over the model. The two situations may be linked.

Use a Separate RGBA node to regain your alpha from the render layer then use it’s alpha socket as the alpha input on a Set Alpha node which is placed at the end of your effects chain.

I shall try this.

BTW, I figured out the root of the problem. Apparently “Lens Distortion” doesn’t like transparent backgrounds. As soon as I removed those nodes, I got my transparency back. However, it adds a lot to my effect, so I’ll try your proposed method. Thanks!

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Update: I tried your method, and it didn’t help. I’m assuming that I did it wrong though, so I’m uploading a picture of the progress. I guess people will catch on to what I’m working on as well XD.

Worse comes to worse, I have the work around that I found earlier. That being said, the color abberation effect that I get from Blender is so much better than what I can achieve using basic methods in After Effects.

I tried responding a few hours ago. I guess I must not have submitted the post.

It didn’t really seem to work, but I’m assuming that I did it wrong. It’s not really a problem though. My plan A was to add my background in After Effects, but what I’ll probably just do is create my starfield inside of Blender. I was a little worried as I’ve been told that it’s a little weird when animated. Here’s a snapshot of the updated nodes with your suggestion. I still think that Lens Distortion is the root cause of my problems.

You get to see what I’ve been working on.

I’m sorry, sometimes I need a post like this one to slap some sense back into me. Try it like this: alpha and image on separate but equal lens distortion nodes then recombine with set alpha node…