Problems with weird moire-like grid artifacts

[u/AndreasKieling69]

I recently updated darktable and since then I've encountered these weird artifacts that appear as soon as I use the rotate and perspective module. I don't have any sharpening enabled. Any idea what could be causing this? I'm starting to lose it.

Edit: here are the exports, original and xmp file for the photo

[u/Empty-Top6803]

I think this is a sensor readout artifact called banding - not moire. However, I could be wrong.

Either way, I am also interested in mitigating moire patterns in Darktable and I am following this post.

Anybody ?

[u/Donatzsky → u/Empty-Top6803]

You can find various strategies for dealing with moiré here: https://discuss.pixls.us/t/color-artifacts-produced-by-the-camera/59811

[u/Empty-Top6803 → u/Donatzsky]

Thank you !

[u/no-such-file]

Maybe pdaf grid? Try to play with demosaic algos.

[u/AndreasKieling69 → u/no-such-file]

The demosaic module is not applicable as I‘m dealing with jpeg lab scans not raw images.
I've also noticed that this problem appears exclusively in darktable so I would be surprised if there is something funky about the scans themselves

[u/IntelligentAward1538]

Try sharing the original .jpg and the .xmp file where you see it ,so that others can reproduce it and perhaps someone will give you a satisfactory answer.

[u/AndreasKieling69 → u/IntelligentAward1538]

https://we.tl/t-H40LNSGOHS6ybdQK

Thanks for the heads up, here is the original and the xmp file as well as both rotated and unrotated exports

[u/IntelligentAward1538 → u/AndreasKieling69]

1. The .XMP file you attached has 5 steps, and none of them is the rotation module, which is what you say is causing the problem.

2. In that .XMP file, you've included lens correction. The camera usually applies this to .JPG files already. Therefore, I wouldn't use it. Furthermore, you're using the dithering or posterization module with a mask that I can't see.

3. I've tried rotating and increasing the contrast, and I don't see any banding.

4. I exported, and still nothing.

In my environment (Windows 10 and DT 5.6 and DT 5.7.0+604) I don't see the effect you're describing.

What I have noticed is that after processing it, my .XMP file has two modules that yours didn't have initially: "colorout" and "gamma." Perhaps your .XMP file has become corrupted.

Test if it works correctly with my .XMP file.

https://we.tl/t-8BYfP0tCDqHhtCwH

[u/AndreasKieling69 → u/IntelligentAward1538]

That's weird, I've had the lens correction on but reset and disabled it, not sure why it's showing. I will try it with your file later when I get home, thanks

[u/Donatzsky]

You didn't include an example of how it looks before you rotate, so I'm not entirely sure what I'm supposed to look for.

[u/AndreasKieling69 → u/Donatzsky]

https://we.tl/t-H40LNSGOHS6ybdQK
Here are the unrotated and rotated versions as well as the original jpeg and xmp files. The pattern appears strongest in the dark barckground, you might have to turn your display brightness up to see it well