I had a photo in the general gallery. the sky was a little too bright. I used the program Gimp, which is a detailed free program similar to the abilities of photoshop. I created a mask, I changed the levels, so the church was dark and the sky was light. I then selected the church. I got back to the original photo. I then changed the brightness and the contrast. It looked good. Then I inverse selected, and edited the sky. I had trouble changing the brightness in the clouds without it looking horrible. Then on closer inspection I had a thin green, or just a line around the whole church. How can I stop this from happening.