Haiku uses a custom vector image format to store icons… The goal of the Haiku Vector Icon Format (HVIF) is to make vector icon files as small as possible. This allows Haiku to display icons as several sizes while still keeping the files small enough to fit into an inode (i.e., inside a file’s metadata). - article

For comparison : 500bytes vector image =  500 bytes
128x128x4b images (pico8 screen)       = 8ko

see also

• Icon-O-Matic - describe path feature of the Haiku icon vector format
• Haiku icon is the best format - discuss portability to other system