Windows doesn't fully support png desktop. when you set a png as your desktop it compresses it quickly to a supported low quality format. Also using png files with the desktop slideshow slows it down each time it goes to display them because it needs to convert the image each time. So I save them as high quality jpg which it supports and it looks perfect on my 1920x1080 desktop The preview for the image above is blurry because it is being compressed by diviantart to fit in a smaller spot, the full download is fine.
When I first drew the scene from the show [link] I wanted to draw more like it so i started drawing wallpapers similar to its style for the other 5 ponies. When i finished the last one i went back and looked at that first scene of pinkie pie i drew, but it didn't quite fit right with the others. So i decided to re-draw Pinkie Pies to make it match in with the theme and color layout of the other 5.