This video illustrates how the G'MIC filter 'Contours / Extract foreground' can be used to quickly extract a foreground object from background, in an opaque RGB image.
Beware, this filter requires at least version 1.6.0.1 (beta) of the plug-in to work properly.
Get the latest stable version of the G'MIC plug-in for GIMP at : http://gmic.eu/gimp.shtml
Get the latest beta version of the G'MIC plug-in for GIMP at :
https://sourceforge.net/projects/gmic...
Credits:
Image of the penguin by Christopher Michel (https://www.flickr.com/photos/cmichel..., distributed under CC BY-NC 2.0.
Music: "Gander in the Pratie Hole, Morrison's Jig, Drowsy Maggie" by Sláinte (http://www.irishband.com/slainte/inde..., distributed under CC-by-SA.