In the question Display partial PNG? the problem is not to access the PNG file format in the way usually used for computer graphics, but to access a truncated file in a way it was not designed for.
I'm assuming that questions about computer graphics file formats are on topic in general (please make that a separate meta question if there's any disagreement on that). This meta question is just about whether they are still on topic in this non standard usage which seems to relate less to computer graphics.
Should such questions be part of our scope?