The image editor is meant to just be a basic image editor, because there are plenty of powerful (free, even) image editors you can use and so the C2 developers can focus on making C2 better instead of remaking photoshop.
There's not an all-in-one button for it, but you can save your image and then, of course, open it in whatever program you like.
The manual also states that "the image editor is currently a work-in-progress and is not yet feature complete."
Yes, it could be better, but priorities and all that..