Addition layer semi-transparency

Question

I'm trying to export a semi-transparent png. There is an addition layer with giving a bloom/glow(not really sure what to else call it) which shows up fine when there is a black background, but disappears when I hide the layer and/or export it.

I had a very similar problem in blender when making the model while exporting it. The only way to properly get around it was to export two layers, one with traansparency and one with a black background, and then in gimp reduce the lightness of the layer with transparency to zero, and set the mode for the layer with the background to addition.

I want to be able to export this as semi-transparent so I can composite it over a video without the hassle of having to export two files and set them up in the video editing.

Here's the file if anyone can help :)

With black background Without background (no bloom/glow D:)

Answer 1

This is normal, most layer blend modes (Normal is one exception) keep the opacity of the pixels over which the new layer is applied.

• When you have a background (Layer layer), all the pixels of the stack (composition of Layer and sunT.png layers) are opaque, so all the pixels of your sun.png apply to opaque pixels and have a visible result.
• When you remove Layer, for the black background and the glow the application of the sun.png blend mode occurs on pixels that are transparent in sunT.png, so the result is transparent. This is also why the black background in sun.png disappears in that case.

If you want a glow, add it in a layer below your sun and keep everything in Normal mode:

Result (without Layer):