Huge potential  simple yet powerful and fast  without ads or asking for unnecessary permissions  but here are few things that could help making this my default gallery app: 1- the option to make the background black only when in preview mode (when the status bar etc. hide away). 2- double tapping to zoom making the photo pixels match the pixels of the phone display in 1:1 ratio. 3- perhaps a 'material design colours' pallette for choosing colours in the theme/customisation section?