>>716055323Online tools might also be doing things you don't know about.
I tried tinypng quickly with a digital illustration I had on hand, and whilst pinga losslessly compressed it to 887kb, tinypng used lossy compression to get it down to 291kb, and I could identify some significant color information was lost and checkerboard artifacts were introduced.
Perceptually, this is fine and you'd never notice unless you look real close or compare original files, but it's shit for preservation or for use in editing.
Tinypng's lossy output was also ironically not maximally optimised, I could compress it a further 1.2kb using pinga.