I've spent a few days (approximately 15 hours, I'm retired) trying to resolve this GIMP issue by reading, watching YouTube and experimenting. I'm sure it's a very simple issue for anyone with knowledge of graphics software but I am completely baffled and I would appreciate some help.
I have created 3 landscapes and I have successfully added them to Stellarium. I can now select the viewing areas around my house. What I cannot do, and has been so frustrating, is to black out the transparent selection below my centered panorama so that I don't see stars below my horizon.
I know how to open my JPG, resize the image and transparent canvas, add an Alpha layer, remove the sky and create a PNG file in the appropriate folder, but I cannot paint out the bottom of my canvas.
If someone can point me to a good tutorial for this, or just tell me the steps (the manual was not helpful, it really assumes a knowledge of graphics software) I would really appreciate it. I believe it has something to do with layers, but in all the videos on YouTube (both GIMP and Photoshop) it looks like there is a quick button click and the paintbrush is used to paint out the bottom transparency.
Any help would be most appreciated.