There are times when you want to fiddle with a bitmap without necessarily wanting or needing to bring the full force of Photoshop to bear.
At times like those, if you’re on a Windows box, Paint.NET fits the bill nicely. While lightweight, it’s neither crippled nor a toy. It’s available free of charge, and you can download the sources if you want to hack on it. This might be my occasion to develop at least a working familiarity with the .NET framework.