Sure, you can edit photos on a smartphone, but even "giant" 5-inch displays are far from optimal for the task. A full-sized slate is a much better tool for image editing, and Snapseed is a great choice for tablet-toting photo buffs. While iOS users have enjoyed Snapseed for some time, the app is relative new to Android. (Brief backstory: Google bought Snapseed developer Nik Software last year and brought its image editor to Android.)
Snapseed provides photo-manipulation essentials such as single-tap auto correct, cool filters for arty expression, and smooth integration with Google+ for easy photo-sharing. Of course, it's not the only photo editor for Android, so be sure to check out popular competitors PicsArt Photo Studio and PicSay Pro as well.