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I'm trying to export my renders in EXR format for some further compositing in nuke, but noticed that the files exported as .exr look very different to the files exported as .png or the Blender preview.

After some searching, I found out that pngs are unable to correctly display emission and transmission for the same pixel, but that effect is actually what makes the crystals in my render look good, so in the .exr files, they look extremely flat.

Is there a way to export exrs in a way that would result in the same result as from the png file? (Aka force exrs to produce the same "error" for pixels with transmission and emission data)

PNG: enter image description here

EXR:enter image description here

For reference, the EXRs contain these passes:
• Diffuse (Direct, Indirect, Color)
• Glossy (Direct, Indirect, Color)
• Transmission (Direct, Indirect, Color)
• Emission
• Object Cryptomatte

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  • $\begingroup$ You have all the data from the render in the EXR files. What stops you from compositing the images any way you want? In any case, you have not provided enough information about what you are doing. What passes are you rendering, how are you compositing? What software?.. Please edit the question and provide full context. The question is not possible to answer as is. I am voting to close it based on it's current state. $\endgroup$ Jun 19, 2023 at 14:31
  • $\begingroup$ I updated it with the information you requested :) $\endgroup$
    – Aci
    Jun 19, 2023 at 15:17
  • $\begingroup$ So you have Transmission and Emission passes. So what is stopping you from adjusting them whatever way you like? Another important thing to note is the fact that Blender saves color management transforms to png format, while EXR contains raw untouched data, so png images benefit from filmic color transform that might contribute to the look a lot with your scene. The fully saturated colors in light sources look quite unnatural. You might want to address that somehow in Nuke. AgX would help a lot here if you composited in Blender. $\endgroup$ Jun 19, 2023 at 15:31
  • $\begingroup$ The issue is that the way PNG exports look is the result of a bug / limit of the file format, and I have no idea how to recreate the effect in the exr format, which is why I'm asking if there's a way to export a file making use of passes and layers while still getting the same look I get from the PNG limitations. $\endgroup$
    – Aci
    Jun 20, 2023 at 18:28
  • $\begingroup$ What PNG format bug are you referring to? I am not aware of any. Could you provide a link to the source of this information? Could you share an EXR file and a png file maybe? $\endgroup$ Jun 20, 2023 at 18:50

1 Answer 1

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My best guess without seeing the EXR file about what is happening:

The PNG file is saved with color management transforms baked to the image. In this case it is Filmic and it compresses high dynamic range especially the highlights. Also it should desaturate highlights slightly. And that's exactly what we see in the PNG compared to EXR in your provided images.

Your posted image of EXR looks like it lost detail in the highlights and highlights are completely saturated so that's maybe what could happen if you take the data in EXR and just display it as sRGB without any additional color transforms that would compress high dynamic range this way clipping all the highlights that do not fit. It looks like you need better color grading in Nuke. You could use Filmic color transform in Nuke as well since Nuke supports OCIO, or do whatever things that are done in Nuke to deal with issues like this that I do not know about since I don't use Nuke. To check if that is correct, just drag and drop the EXR in the Compositor in Blender, and have a look how it is displayed with regular Blender's Filmic color management. It should look the same as PNG since the EXR has all the data and nothing is actually lost there, but it is just displayed wrong in Nuke.

You could also do your compositing in Blender or at least consider it. This way you can be sure the colors you see in Blender will be the same during compositing without any extra trouble.

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  • $\begingroup$ Thanks for your help! :) $\endgroup$
    – Aci
    Jun 24, 2023 at 11:07

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