TL;DR: How can I properly save a picture with semi-transparent "emit" pixels coming from a bloom? I understand that .PNG can't handle that, but I'd expect TIFF/Targa/.EXR to handle it properly... and they don't (see below what I tried).
When generating an image with bloom (here some simple cubes in EEVE) and transparent background (see that I'm also using the default Filmic profile):
I can't find a good format to export it, in such a way that I can directly use it in other softwares to display it on top of other figures (if possible, I'd like it to work with Krita, Gimp, but also if possible in game engines like Godot or Unity, or (in my dream) in LaTeX/TikZ…):
What I tried:
.PNG does not work because it uses only straight alpha (so it means that it is impossible to have a "emit" pixel which fully transmits the light and also adds some colors). As you can see, all semi-transparent "bloom" parts are removed (I added here a black background):
.EXR (OpenEXR) are also not ideal: as I understand, they contain basically RAW data (linear space, ie colors basically belong to
[0,+∞)), but they can be interpreted in many different ways, and I can't find any software that can accurately open it. For instance here you can see that the blue cube has bad colors in Krita (more precisely, it is displayed like if the "View Transform" in blender was configured to Standard instead of Filmic):
I tried to setup OpenColorIO with "filmic" in Krita (
Parameters > Dockers > LUT, then taking the OCIO configuration from
<blender install path>/2.92/datafiles/colormanagement/config.ocio):
but I get an error when I load the filmic view (and often a segfault later):
Error The specified transform file '/nix/store/pzi5xl05mifb53apxz6vhqmz7xp8zi66-blender-2.92.0/share/blender/2.92/datafiles/colormanagement/filmic/filmic_desat65cube.spi3d' could not be loaded. Not enough entries found. sending event 3 to object qt_scrollarea_viewport
If I open it with gimp, it's even worse, all semi-transparent area are removed, and GIMP does not support OCIO:
So .EXR files are really not ideal to work with, and I guess I've zero chance to make it work in Unity/Godot/LaTeX if softwares like Krita/Gimp can't open it properly.
Targa or TIFF The Targa and TIFF format are supposed to handle premultiplied alpha (this one allows us to have emit pixels), so in theory it should work (I guess)... but in practice it's not working better than .PNG, like if blender uses premultiplied alpha instead of straight alpha:
Here is an example with TIFF
and with Targa:
Is it a blender bug that Targa/TIFF output does not properly render the emit pixels? Is there a way to get a format (if possible quite widely used and that do not expect me to properly configure OCIO) that accurately represents the "Filmic" view given by blender? I'm desperate enough to accept convertion via imagemagick...