>>535619237
>I haven't searched for a way to autodetect the black bars though.
Well damn, that was easy.
I just ran
>mogrify -bordercolor black -trim
on >>535608905 and got this.
I suppose this might fail if an entire side of the image has perfectly black pixels beyond the edge of the pillarboxing, though. I might get some funky screenshot sizes in really dark games if I add this post-processing to my screenshot script.