Some effects [bloom, smoke, fire, ..] still don't save in PNG with transparent background (occlusion vs. emission) #81199

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: 83dc97ccc0
Worked: (newest version of Blender that worked as expected)

Short description of error
https://www.youtube.com/watch?v=mQqV77PaOVs&t=84s
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 BLOOM BUG.blend
2 - press F12 [render]
3 - save result in PNG
4 - open result in any paint software and put under result layer any colour

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Added subscriber: @Jeroen-Bakker

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.

@Jeroen-Bakker 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?

If I simply draf-n-drop to the viewport - it looks like this: http://joxi.ru/zANYDG1CvLnQK2?d=1
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)

Added subscriber: @jenkm

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

Changed status from 'Needs Triage' to: 'Confirmed'

Added subscriber: @brecht

Did some research and had a design discussion with @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.

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Added subscriber: @Francesco-Della-Torre

A similar issue is happening in this video: https://youtu.be/kxgH2whhc8g?t=41

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@Jeroen-Bakker any update on this issue?

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Added subscriber: @Bradley_G

Added subscribers: @Vido, @mano-wii

I tried to save render to .exr, .tga and .tif all I get is empty image, just check board

Added subscriber: @iulian.flester

I believe this problem can be easily solved if you do what Photoshop is doing. Merge the layer that has the overlay with an empty one, or how is it called? rasterize? Because if I hit render I can see the final result perfect. The problem starts to show up when you do the saving. So what if you could add a node that will rasterize the image. Then you could save it or do whatever else you need.

Added subscribers: @Rui_Martins, @PratikPB2123

Added subscriber: @blix409

Has this issue been solved for Blender 3.1? I'm having the same issue and not sure why i'm not able to save png with emissive fire.

Added subscriber: @Zoni

Added subscriber: @Ulf3000

Added subscriber: @zachnfine

Eevee's bloom doesn't seem to affect the resulting alpha channel of any exported file format that supports alpha -- I've tried ffmpeg->QuickTime->Animation, png, and OpenEXR from Blender 3.0.1 on Windows 10 Pro (10.0.19044 Build 19044). My test project includes some bright emissive objects that look very anemic without bloom.

When writing multilayer OpenEXR files, with a Bloom pass encoded as one of the layers, the resulting 'combined' layer has an alpha channel and no visible bloom effect, and the Bloom layer has no alpha channel and is just on black.

As a workaround I tried using AfterEffects to add the Bloom back over the Combined layers of a multilayer EXR export, but I couldn't get it to look exactly like my temp comp inside of Blender.

Now I'm giving this workflow that uses Blender's compositor to add the Bloom layer to the alpha channel a try. (https:*blender.stackexchange.com/questions/200068/blender-eevee-how-to-render-bloom-effect-when-using-transparent-background)

Added subscribers: @AndreasBecker, @Ethan-Hall, @OmarEmaraDev

Added subscriber: @Iago-Diogo-de-Vasconcelos-Mota

In #81199#1023863, @Jeroen-Bakker wrote:
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.

This is very true.

The standard way that the PNG alpha is interpreted is "unassociated" or "non-premultiplied."
This type of alpha blending, only allows the PNG to darken the underlying image.

PNG Alpha Blend	Proper Bloom

Added subscriber: @P387-1

Added subscriber: @Yuro

Trying to render out images for a website, where the image needs to be separate from the background and can't use an Add blend mode.

I couldn't find a solution when using eevee bloom to achieve this result. Ultimately we need the glow in the alpha of the saved image. The goal should be to save from Blender, achieving the same result as adding glows manually in a 2D package. Is the way Blender is storing the glow internally preventing it from being saved in a particular way?

I had to render my glowing objects in a separate pass then recreate the glows in a 2D package. As Blender is a tool for multiple uses -not just film and compositing- addressing this would be really helpful.

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Added subscriber: @zargul

This issue still stands as of Blender 3.4.1, Snap package. Using the glare node in compositing instead of EEVEE bloom does not fix the issue, and it is consistent across EEVEE and Cycles, so it has to do render saving, and not EEVEE particularly.

Added subscriber: @dursunumit

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Some effects [bloom, smoke, fire, ..] still don't save in PNG with transparent background (occlusion vs. emission) #81199