@Psykatte If it's a 4-color palette, then to save file size turn it into an indexed PNG rather than a 32bpp or 24bpp PNG. With only four colours that's essentially 2bpp so 16 times smaller.
@TerrorBite As it turns out I already had a 4k copy compressed like that laying around and it's 1.6MB. I also only just process how counter-intuitive it is to call it HDR when it uses a 4-color pallet. lol