Sometimes it happens that I would like to extract a person from a photo and remove the background. How can I do it with GIMP? Every attempt that I made gave me very bad results.
Can you give me some steps to follow?
With most things in Gimp and Photoshop, it comes down to using the selection tools. The better you get at using selections, the easier time you have removing/extracting elements from the background.
This is a pretty good step by step article on how to use the selection, masks, and feather tools to get a good selection around your subject.
Removing backgrounds in a photo that wasn't specifically shot for the isolation is usually a very complex process. There are many completely different techniques to isolate details, all depending on the subject itself. One thing is to isolate evey single hair of a lady against a forrest background, another is to isolate a sharp car on a blurry road.
See The Russel Brown Show, he's one of the Adobe Photoshop team members, he's got a lot of free video tutorials on different background isolation techniques.
Many of these techniques can be fully implemented using Gimp.
I am not Gimp guru. There is a simple trick I learned which helped me a few times.
(warning: this only works with images with the more or less same background color distinct from colors of the subject)