Darkroom 3 - The fastest and most powerful photo editor for iPhone
Darkroom makes it easier and faster than ever to develop the perfect look for your photos. Skip the import process and start editing in our refreshingly simple interface. Make and edit filters with using our powerful yet easy to use Premium Pro Tools.

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Been using Darkroom ever since the very first beta (personal connection with the developer), and it's been consistently solid. For some things I might open Snapseed (healing, face enhancement, adding grain), but I keep coming back to Darkroom in the end.
Pros:It's fast, good filters, powerful manual controls, well-maintained.
Cons:Wish it had a spot healing feature.