You must close and reopen Paint.NET. The plugin will not appear while the program is running.
: Copy the area, paste it as a new layer, and merge it down to fill in semi-transparent gaps. How to Install Plugins Download the .dll file from the Paint.NET Forums. paint net alpha to 255 plugin download
Run Effects > Noise > Median (radius 1) to remove single-pixel transparency noise before forcing Alpha. You must close and reopen Paint
Not natively. But combine it with the Batch Processor plugin (separate download) to apply Alpha to 255 to entire folders. paste it as a new layer
: A built-in adjustment in recent versions of Paint.NET.