Is there a FLAC equivalent for digital comics?

I’ve bought enough digital comic bundles now that they’re starting to take up a decent chunk of storage space.

What I’d love to do, if possible, is losslessly compress them all down to their minimum sizes, in the same way that FLAC does with music. Is this a thing? And if so, what’s the best way to do it?

If lossless compression isn’t possible, is there a lossy compression that’s effectively lossless in that I won’t be able to tell the difference anyway? Lossless compression gives me good piece of mind, but the storage savings from an invisible lossy one are honestly quite appealing too.