Natron EXR not compatible with Blender?


Have anybody problems with EXR from Natron to Blender? Is there any known issue?

I’m on a rush with a job here and we’re working with both Blender and Natron for compositing. The problem is that when I render an EXR sequence in Natron it makes Blender behave slow and sometimes even crashing at import.

If I import in Blender as a sequence (not a single image) I can see the image during the compositing, but whenever I hit the render button in Blender, it delivers a blank render.

I’ve tried different EXR render settings, nothing seems to work. Any ideas?

I can give much details later, but I’m on a deadline and the job has an NDA so… It’s not as simply as sharing my project :frowning:


Ok, it looks like a bug or something. Not sure if report it to Blender or Natron. I had this simply UHD project.


I’ve exported to EXR with default settings and when I try to import to Blender… it crashes.

Can anyone give it a try?


I gave it a try. Lots of problems. Natron seems mostly okay though.
First off I’ve recently realized how to use the Filmic addon for Blender Color Management

Not that this shouldn’t matter but it might help.
I use it to set the OCIO from Natron’s, which for me is a ‘blender’ one provided (check try that too)
C:/Program Files/INRIA/Natron-2.3.5/Resources/OpenColorIO-Configs/blender/config.ocio
to that new one replaced in blender
C:/Program Files/Blender Foundation/Blender/2.79/datafiles/colormanagement/config.ocio
that is used in Blender so it’s just setup probably makes no difference.
[ First issue in Natron is Project Settings Output Format is not retained when reloading files ]
My write node has sRGB EOTF for input as the color bars is useless in this regard anyway but the mighty proper Filmic Log Encoding for output.
I put Bit depth 16f for floating point. Not all plans which makes one finally ask why are you using EXR? are you expecting Planes in Blender from the EXR for different material properties?
Loading these into Photoshop shows a washed out 32bit image I guess because they can’t handle 16f properly and see it as 32i (probably?). Alas the range is mid 66 to 189 in levels adjuster gets you back to semi-normal in that case.
In Blender I tried with the Natron blender OCIO and it was always the file not found magenta. I even used the compositor (with Natron blender color managements OCIO EXRs) where you can see the exr or I also did PNG sequences and it still showed magenta from the Viewer (compositor output) Node (which is how you link the compositor to be a texture).
Using 32i makes Photoshop show white, so they/Adobe seems to have F’ed that, but Blender still sees it (using Image Texture node’s Auto Refresh switch to be sure?..!)
Still it’s washed out for the same reasons 16f is in Photoshop color space issue.
16i is the same as 16f in photoshop. Let’s leave photoshop out of this I was just testing to see what was in the image but it loads all bit depths as 32 bit with not top or bottom third.
Okay so maybe though that proves Natron is not putting out bit depth properly because Blender sees the same shyt. Probably because of EXR overriding it or something.

I mean again with my first counter-question in mind, I’ll just say use PNG if you need the alpha, (which simple colorbar’s alone are not testing.)
Then you can get 16 bit checked off (with RLE compression level 7 not an issue) and colorbars is still flat but it’s slightly darker in Photoshop.
With PNGs you don’t have to worry about using the same 3rd Party OCIO to get EXR working.
Next I offset the colorbars to see what’s happening with alpha. The alpha in the PNG is there is Photoshop but in Blender you’ve got to battle with the shader node tree as that’s not automatically understood by Blender like you might expect either. Then you’ve got to invert the alpha to a Transparent BSDF Node (in cycles obviously). Use a Mix shader with the original Alpha as Fac if an Emission Shader for color is plugged into the bottom (or the inverted version if top) with the transparent shader node.
Note it was all tested with an image sequence.
[Natron seems to have problems overwriting EXRs or at least it seemed to rewrap with only a transform of the colorbars so I had to merge a copy over top to see the file change, so it looks like some more bugs but not sure on that at this moment.]
Okay so eventually you can do the same shader trick to get EXRs with alpha too.
Further Notes since no file uploads here?! Emission Strength is 0.5 and alpha only visible in rendered mode (Material mode shows white).
Let me know what made a difference for you.


Hi @MasterJames! Thanks for your time.

I’m not sure of some of the things you told. I’m gonna need a second read on that.

I need to export in EXR because we’re working on a VFX pipeline with digital cinema footage. We need to have a linear float point workflow.

I’ve tried to change the OCIO config files but the results are the same: if you export an EXR from Natron, Blender is not going to be able to open it :frowning:


No I did do it. It can be done. Depending on the format written out I suppose. Make a smaller test like you did follow what I said (if possible I know it’s a path of discovery with lots of details of what I did because it’s unclear where the glitch up is). Maybe make a post on a Blender site (like Stack Exchange) and cross post it here and pick one that will allow file uploads so I can send my example files.
Oh there was one other thing I didn’t think would matter much but I was also going to check that too (but forgot and haven’t yet) and that’s that I have done this only on Natron version 2.3.5, but I’m sure 2.3.10 is similar. If you’re not updated to that maybe try that too.

Also note that if you’re not using Filmic Log Encoded you should reconsider (or at least there is a strong argument to make). Also PNG can have the same data too so I’m pretty sure you can make it work.
I suggest you first review this sufficient Blender Guru explanation and then also know as much as possible about ACES

I would say it’s more Blenders fault anyway. Can you open your exr images in Photoshop.

Final word is I thought maybe you should be using Nuke for what I think you’ve described comping since it has a 3D camera system and tracking, etc. Does nuke or aftereffects see your Natron EXR files?
You could further try your luck with Blender 2.8 although I realize that’s not recommended, unless it makes a difference and actually works.


Also noted a few more reasons you might not have got it to work like I did.
You want both Blender and Natron to have the same OCIO.config and you probably need to restart them to be sure it’s properly loaded.
I’ve added other considerations in my second response like the Version Number I used as further possible discrepancies to consider.