By default, Windows 10 compresses JPEG pictures you use as your background, reducing it to around 85% of the original quality. If you’re bothered by the compression artifacts this often introduces, here’s how use high quality images instead.
We’re not really sure why Windows 10 compresses background images. It’s not like doing so saves tons of disk space, and using better quality images doesn’t really use up any system resources. It may have something to do with syncing them between PCs that share the same Microsoft account, but even then, not much space is be saved by compressing them. The really interesting thing is that background images used for your lock screen and sign in screen don’t appear to be compressed at all. Here’s how to replace your compressed wallpaper image with a full quality image in File Explorer, and how to turn off compression altogether in the Windows Registry.