Not the parent so I can’t tell you exactly what he did, but some suggestions: - The PNG specification contains plenty of information including width and length

Not the parent so I can’t tell you exactly what he did, but some suggestions: - The PNG specification contains plenty of information including width and length that allow you to use 2d arrays rather than ArrayLists - The RGBA 32bit integer doesn’t need to be unpacked.. you can just perform shifts and transformations of each of the 8bit channels. - If you do unpack, you should use native 8bit unsigned ints - You don’t need an unmodified copy.. that’s your file - Undo stack should contain deltas, not the whole image over and over again. Edit: formatting