OpenEXR export … color channels shifted in generated EXR file

[leonard7e]

Material Maker version:
Version 0.97, this build:
https://github.com/RodZill4/material-maker/actions/runs/1431815396

OS/device including version:
Ubuntu Linux 20.04
GPU: RTX 2060s

Issue description:
OpenEXR generated from MaterialMaker has mismatching colors.

Testing colors, it seems that color channels got shifted like that

Alpha → Red
Red → Green
Green → Blue
Blue → Alpha

Steps to reproduce:
Just export OpenEXR from Viewport2D and check the result.

I prepared something which might be useful. Load test_colors.ptex file from there …
https://drive.google.com/file/d/1xlusZCEib_18czDcPqSpfDDlG5re3D-_/view?usp=sharing

There are float nodes for 0.0 and 1.0, which could be connected to a Combine node. Plug floats to different inputs of the combine node, and export an EXR file from the Preview2D of the Combine node.

Use Gimp (or other software which supports OpenEXR) to examine result EXR file.

[RodZill4]

Hmm I don't understand this problem. Godot reads the generated files correctly, and Godot's code seems to handle channel order.
No problem with exports? It's exactly the same code...

[leonard7e]

Same problem with material export.

For some reason the alpha channel seems to get at the wrong side of the RGB data block.

The MM file I shared helped me to discover that RGBA channels have been shifted in the EXR image. I needed to extract EXR image from Preview2D, because that way the Alpha-channel survives export.

[leonard7e]

Another test-setup for MM, much cleaner and simpler.

The MM file … test_color_channels.ptex

Original image …

Exporting this image would result in distorted colors in the EXR file. To balance it out, the channels are shifted with "Swap channels" in opposite direction:

The EXR export of the image above (first row's alpha is zero) does show the correct colors, the same colors as the original image.

I do not have an idea how it happens, but I guess, it is evident that the channel shift in EXR export happens. And it causes the color distortions I could observe in EXR export files.

[RodZill4]

I want to investigate the issue in Godot (without any MM code). Godot seems to read the exported EXR files just fine.

[leonard7e]

I tried in a minimal Godot project. Godot reads MM generated EXR file's colors fine.

But the same is not true for other software I tested. I tried exrdisplay, Gimp, Blender, Natron2 and DaVinci-Resolve.

If possible, try exrdisplay. (exrdisplay is from makers of OpenEXR)

Comparison …

Screenshot Godot

Screenshot, same file, exrdisplay

[darthLeviN]

same problem here. in the previous version (0.95) blender export wasn't working at all, now it just exports wrong.

[leonard7e]

The strange thing about it, this problem won't appear if Godot is used for testing. Godot loads EXR generated from MaterialMaker just fine.
However, EXR files generated by MM aren't working for other apps which support EXR (Blender, Gimp, DV Resolve, etc.). Technically, they 'load', but the channel's order is changed. Sadly, this is a no-go for an EXR based workflow.

Because of the disfunctional EXR workflow, one still needs to move to PNG.

[darthLeviN]

The strange thing about it, this problem won't appear if Godot is used for testing. Godot loads EXR generated from MaterialMaker just fine. However, EXR files generated by MM aren't working for other apps which support EXR (Blender, Gimp, DV Resolve, etc.). Technically, they 'load', but the channel's order is changed. Sadly, this is a no-go for an EXR based workflow.

Because of the disfunctional EXR workflow, one still needs to move to PNG.

i'm not sure about that. i think godot itself handles exr wrong. and it's being exported with the help of godot libraries (is it?) then it will be just wrong...
i open the exr images with gimp. decompose their color channels and their wrong.

[leonard7e]

I checked EXR generated from Godot. You are right, it's Godot. My little Godot-Project does just load an RGBA png file and export it as EXR (if button pressed). Generated image had wrong color channel order; exrdisplay reveals.

MM just uses Godot to generate EXR files.

I created a new issue in Godot's Github project.
godotengine/godot#55472

[fire]

Made a pr. godotengine/godot#56715

[leonard7e]

Thank you very much for your help.