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2.8/2.79 Bug: Glare Effect in Compositing Not Working with Transparency in Cycles/Eevee
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Description

System Information
Windows 10 64-bit, Geforce GTX 970, Intel Core i7-6700k, 16GB Ram
Blender Version
2.80.0
Date: 2018-08-11 18:54
Hash: b4b8d3ab0e4
Branch: blender2.8

Short description of error
The Glare effect in Compositing does not work properly in both Cycles and Eevee when using transparency. This issue also exists in 2.79 versions.

Exact steps for others to reproduce the error
Select the render engine of choice, choose PNG for the output with alpha included, enable the Scene's transparency in Film, then render image.

Details

Type
Bug

Event Timeline

Bastien Montagne (mont29) triaged this task as Normal priority.

I guess that’s something to do with premultiplied/straight alpha, @Jeroen Bakker (jbakker) care to check? Thanks.

It might have something to do with it. This was pretty much the closest workaround solution I came up with, even then there's still some compromise. Is it a compositor/viewport problem or is this just normal for some effects in Blender? Sorry, I'm still fairly new to Blender.

The compositor actually works fine, but the image editor is not displaying it correctly, see T52680.

If you composite the result over another image or save as OpenEXR it should work fine.

@Brecht Van Lommel (brecht)

The problem lies elsewhere.

The render has zero alpha, outside the object.
After the Glare effect it remains zero.

That is, the Glare node does not take into account transparency.

The fact that is has zero alpha outside the object is correct, it's intended to add glow without obscuring anything behind.