Wallpaper resolution confusion

[steve_ma]

Hoping someone can fix me as I am having trouble figuring this out. My downloaded wallpaper seems to end up looking rotten. Like ill defined and pixelated. Like I'm using the wrong resolution. I am using 720x1280 jpgs, which I thought was the right size/resolution for non scrolling wallpapers. I have downloaded a couple of the HD wallpaper apps in the past (which seem to work fine, BTW) but I really like some of the stuff I can find online better. I have a non-rooted vzw Galaxy S3 with all current updates.

Any thoughts appreciated.
--Steve