I tried a quick recompress of the PNG which generated this image (same pixels/RGB values, just adjusted compression):

Looking at the metadata, the gamma value is pretty different. If I remove the gAMA chunk only, it similarly looks better:

I guess probably we should be ignoring the gAMA chunk here? Its current value is 22727, which is what causes things to be darker.

-[Unknown]

Nice, yeah, indeed seems very likely that the PSP simply ignores the gamma block entirely, and thus we should do the same when displaying these. Don't know if there's an option for it for the png reader we use.

Doesn't look like there's a way to override gamma in the simplified API that we use (png_image_begin_read_from_memory). We'd have to switch to using the absolutely awful full API to access the gamma modification functions..