There are hundreds of photo editing tools on the app stores.  If you looking for a PRO set of features that allow you to dial in on image Refinement, Darkroom App is a top pic.

Features that set it apart from basic photo editing apps include the ability to adjust perspective. If you have a photo with an awkward tilt you can easily adjust the view.

With filters you can dial in the exact desired result with the curves and color channel controls. They are powerful but easy to use.

When you share your photo you can add copyright, as well as, your contact information.

The Core features are free. And you can test the premium features prior to purchase.