Free, open source Image editing software for Windows is virtually non-existant. The only software to fill this niche is Paint.net.
However, with Paint.net's reliance on the .NET framework, it can be slow to work with.

As Imagesoft is written in C and uses the Win32 API only, it is not reliant on frameworks which can become a resource hog.

Imagesoft incorporates many visual ideas for the look and feel of its GUI directly from Paint.net.