Here is another nice image done with Artsy Dream. As you can see (when getting close enough to the monitor and potentially squinting), there are stripe artefacts in the image in the darker regions.
After asking the interwebs about this, it seems that this effect appears when creating images larger than a certain threshold with Flux (or this model in particular). Horizontal or vertical stripes/bars appear when upscaling the generated image (which is usually 1024×1024 in any aspect) to twice the size.
Here is another example of a “ruined” image:
Here are pretty obvious stripes at the bottom in the dark area.
I tried a lot to get rid of this by using different upscaler models other than my usual one (4xUltrasharp), but nothing really helped. Before I knew about the size limitation of Flux, I also tried different sample methods, CFG values and so on.
In the end, I tried using a different refiner model for the upscaling part. After some trying some, I ended up with Flux1.Dev, the original.
Here you can see, that the stripes are gone. Yay! 🙂
Unfortunately, this also alters the contents a bit and I actually like the bunny in the original image better, but it’s better than an image with obvious artefacts.
You can still play around with some values to get the image to look the way you want, maybe try using other Flux models that are closer to the Artsy Dream contentwise.