A major rewrite of the module, circumventing the generic (and probably insoluble) problem indicated in #2908504: Saved size differs from the one delivered by API and #2914964: Image derivative size different from original even in absence of any effect.
A separate branch that uses a new approach to optimizing imagestyle (derivative) images.
Added support for s3fs: #2893890: Does not work with s3fs
The first stable version of the new module; check it out!
Initial release of the new module.