A tool (library, source-code, algo) to select area in an image based on perceived focus plane

Question

Say we have an image in which a human eye can distinctly see several "planes" of focus - a blurry background ("telelens"), the sharp(er) subject (a human, or an object), and again a blurry foreground (if any).

I would think that it is computationally possible and feasible to "separate" the subject from the rest of the image data. I.e. selecting the subject borders, by means of outputting a mask channel that can be imported into say Gimp (I don't use Windows, so unfortunately don't have Photoshop) as a selection.

I would review anything from a finished tool through a library (I am on Linux) down to links to articles and/or review papers that discuss means of realizing the algorithm I have outlined.

Answer 1

Multifocus image fusion based on region selection - IEEE

The basic idea is to select sharply focused regions from source images