"Complexity" of Flags of the countries of the world

Flags (png) from: https://flagcdn.com/w2560.zip https://flagpedia.net/download/images

run:

chmod +x init.sh
./init.sh

What am I doing?

I am trying to zip all the flags (in raw .bmp, no compression) as strong as possible to grasp how the file can be compressed. So, I have the new size if .zip archive and the size of the original .bmp file, and the complexity index would be new size / org size.