Transparent Background Effecting Objects

[Dishcandanty]

Hello! Im fairly new to Blender and I hope someone can help me out here. Not sure if this the rightplace to post this. But its effecting me directly in compositing. I’m working on an object, and I want to have a blurred object behind it. I’m planning on using this object/image with other images that I have already made (compiling them gimp). And so I need a transparent background. The problem is if I enable the Render > Film > Transparent. It effects the visibility of the objects in the compositor!

So the second object behind the first one is then only visibility is what would be on top of the second image. I’ve messed around with the Render Layers toggling the Mask Layers. But it appears only to be the Film Transparency that is effecting it. I’ve tried creating a transparent image for use as an enviromental/background texture, but end up with a black background.

I’ve got the two objects on different render layers, and have been trying to add via either the mix or the add node. It’s almost like blender is assuming anything outside of the first layer is supposed to be transparent… I may not be going about this the right way. Thoughts Tips. Im assuming im missing something simple somewhere and can facepalm with someone elses two setence response.

[BartekSkorupa]

Let me first clarify something. I want to be sure that I understand you:
Image1 has alpha1. Image2 has alpha2. When you use mix node (image1 in upper input, image2 in lower input) resulting alpha is alpha1, right?
When you enable “use alpha of second input” - resulting alpha still doesn’t exceed the boundaries of alpha1, right?

Fine. Now two messages: bad and good:
bad: It is so when using mix node and there’s nothing you can do about it.
good: there is a way to do what you want, but you need to use different node for this. Instead of using mix node, try “alpha over”. If you happen to have weird bright fringe, turn on the option: “convert premultiplied”.
Hope I understood your issue correctly.

[Dishcandanty]

Let me first clarify something. I want to be sure that I understand you:
Image1 has alpha1. Image2 has alpha2. When you use mix node (image1 in upper input, image2 in lower input) resulting alpha is alpha1, right?
When you enable “use alpha of second input” - resulting alpha still doesn’t exceed the boundaries of alpha1, right?

Fine. Now two messages: bad and good:
bad: It is so when using mix node and there’s nothing you can do about it.
good: there is a way to do what you want, but you need to use different node for this. Instead of using mix node, try “alpha over”. If you happen to have weird bright fringe, turn on the option: “convert premultiplied”.
Hope I understood your issue correctly.

Yes that was what I was looking to do. I’m glad you had your rosetta stone while attempting to interpret my explanation :).

And YES! The ‘Alpha Over’ was exactly was I was looking for! Thank you soo much!