I've a large epub library (~100k) and it'time to slim down hd space waste.
Found that "Resize images" in the editor tools is really usefull, love it.
The module works very well with .jpeg but can't shrink down .png with the same effectiveness so I need to export all .png, convert to .jpeg with an external tool and reimport them in the editor ... ONE BY ONE.
Usually I find epub with 30-40 png, sometimes others with ~ 100 and it's a very boring job to reimport, but I can survive.
Yesterday I found a 84 mb epub with 870 .png in it, so it's for it that I write this post.
What about a NEW MODULE in the editor tool like "Transform all .PNG to .JPEG" ?
p.s.: please don't blame me about the loss of quality in the .jpeg, I'm really satisfied with the results.