Windows 10 and later heavily recompresses wallpapers before using them which frequently creates obvious artifacts. Even worse, Windows JPEG implementation loads these images incorrectly, including when viewed in the system image viewer, which introduces even further artifact banding. No other JPEG implementations show this extra banding when loading the recompressed images. These bugs have been present for almost 8 years at this point. The only known workaround is this registry entry. https://old.reddit.com/r/Windows10/comments/nyiec7
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