By default, Windows compresses your desktop wallpaper by up to 85% of its original quality. This is done to maximize performance because most people don’t need a 50 MB image eating up precious RAM. There are two methods that you can use to stop Windows from compressing wallpapers. The first (unconfirmed) method is to use a PNG image file. There have been some reports that on the latest Windows 10 Creator’s update, PNG images are immune to Windows compression. The second method is to add a value in the Windows registry.
Using Windows Registry
To open up the Windows registry, hold down the Windows Key + R. This will bring up the Windows run box. From there type in Regedit.
The first thing you should do is to make a backup of your registry just in case anything goes wrong. To do this, go to File –> Export.
Now, let’s add the necessary key to your registry. Go to the following location:
Right click on the folder that says Desktop and create a new DWORD(32 bit value).
Call this value JPEGImportQuality and set the base to decimal and the value at 100.
Then click okay to apply the changes. Afterwards, reboot your computer and re-apply your wallpaper. The differences will be very nuanced, but your wallpaper will no longer have the compression.
**In your sync settings, if you have your Windows theme synced, you should turn this off. Otherwise, Windows will continue to apply compression to save bandwidth when syncing to other Windows devices.