[sordina]

The binary representation is a neat idea. I found the trickiest part of this problem for me was interpreting an expanding boundary of the considered world: https://github.com/sordina/advent2021/blob/solutions/src/Adv...

[msravi]

> the rest of the input image consists of dark pixels (.)

This key bit of information seems to be missing in the originally posted problem, which your link clarifies!