[KevinH]

FWIW, there are a huge number of applications on every platform to do simple image editing. I really hate to bloat the Sigil code just to duplicate one just for those unwilling to use Open With.

Here attached is a screenshot of Sigil running on my Manjaro Box after using OpenWith with a single right click to open the image from our User Guide in "gwenview". Its interface is very simple and includes everything you can do in Calibre plus more.

I can do the same thing on a Mac with the built-in Apple Previewer.

It could not be simpler.

Are there really no good simple image editors for Windows?

I am just not convinced (yet) adding this in any way helps given the flexibility of OpenWith ot use your favorite editor. You do not need to open images with Gimp or Photoshop just to do a simple resize or rotate.

If you have to do this to lots of images in a single epub, a plugin is the way to go.

All of these tools are available in Python (even gui ones) via PySide6 and Qt or directly in Python via the PIL library, so handling this via a plugin for buld changes can be done.

And Doitsu already has png optimizers and jpeg optimizer plugins to use to do both lossless and lossy file compression.