Hi guys, here is my tutorial, showing a complete workflow for processing M42, The Great Nebula in Orion, in GIMP. The image was taken with Skywatcher's ED80 + 0,85x reducer / flattener and astro-modded Canon 450D. Comments and questions are welcome!

Processing M42 in GIMP - part 1


Processing M42 in GIMP - part 2


Processing M42 in GIMP - part 3