Image Toolbox | F-Droid - Free and Open Source Android App Repository
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A powerful image editing app that allows you to crop, filter, convert, resize, c

I occasionally used the Google-owned (but abandoned) Snapseed for photo editing on Android, particularly of RAW images. Recently I discovered Snapseed has stopped being able to export Jpegs from RAW files, which was the last straw for me. This open source app can, and can do a lot of other useful things too! Might not be 100% feature parity with Snapseed, but good enough for many I think