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GLOWING BLOOM effect still don't saves in PNG with transparency background
Confirmed, NormalPublicKNOWN ISSUE


System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: Radeon RX 570 Series ATI Technologies Inc. 4.5.13587 Core Profile Context 20.4.2 26.20.15029.27017

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-25 20:54, hash: rB83dc97ccc081
Worked: (newest version of Blender that worked as expected)

Short description of error
Here this function of preserving BLOOM effect was released, and now it work both on View mode and render mode. BUT! When you will try save PNG after rendering - you will have same result as in past, without blooming effect saved on alpha channel.
Here is example:

Exact steps for others to reproduce the error
1 - open file

2 - press F12 [render]
3 - save result in PNG
4 - open result in any paint software and put under result layer any colour

Event Timeline

Don’t use png. That file format doesn’t support pure emissive colors. Best to use openexr or any other format that stores colors premultiplied.

We could modify png export to convert the colors, but I Wouldn’t recommend to use these pngs due to other alpha space compositing.

Ruslan (rs2128) added a comment.EditedSep 26 2020, 11:38 AM

@Jeroen Bakker (jbakker) I tried do so(saving in openexr).. and have same result, when opened it in photoshop. If be correct I can get two results. 1st one same as with PNG. Second one with BLOOM but without aplha channel stored (it compleatly dark). What I'm doing wrong?

What happens if you open the exr file in blender?

Ruslan (rs2128) added a comment.EditedSep 26 2020, 3:20 PM

If I simply draf-n-drop to the viewport - it looks like this:
If i open it from camera settings as iimage: same.
Unfortunately I don' know how to open it from UI or Compositor or other places

But if i'm opening saved exr from Image editor - it looks as supposed to be. All as should be (with bloom on transperent BG)

Note that this exr file is "premultiplied alpha". Which most likely Photoshop doesn't support at all.

UPD. There is, for example, the "Exr-IO" plugin for photoshop, it has the "opacity correction to support transparent light emitters" option.

I think we should do some research on other file formats. Identify areas of the pipeline that could support this. In user point of view they just expect it to work. But I need to dive deeper in the image loading writing pipeline. Last time I looked at it it was still very fixed. In that case we could add a different conversion to convert to sRGB

Jeroen Bakker (jbakker) changed the task status from Needs Triage to Confirmed.Sep 27 2020, 8:17 AM
Jeroen Bakker (jbakker) claimed this task.

Did some research and had a design discussion with @Brecht Van Lommel (brecht).

It seems that we can add a similar conversion we do for the image editor when storing images to disk for RGB files. When exporting to RGBA there are still some issues at the borders what makes them unusable. I doubt we this could be mathematically removed.

Loading an RGBA PNG back in Blender shows that there are artifacts near the edges.

Bastien Montagne (mont29) changed the subtype of this task from "Report" to "Known Issue".Oct 15 2020, 11:21 AM