about Gegl
many of the gegl operation are samples and may duplicate what already offered by gimp
But others are quite interesting a example is C2G:
its pourpose is make a convertion from colours to black and white more close to that of human eyes ...and it does
but even more interesting is for me its artistic use, i like use it to correct the greyscale and then to add back the original colours
well...i got the idea from here
http://www.flickr.com/groups/gimpusers/ ... search=c2gand this is a example
BEFORE
AFTER
the grainy look was my choice it could be easily avoided...and you can find much more and maybe better use on that link above
trick is simple
1 duplicate the layer
2 apply c2g to the dup
3 change dup layer mode to VALUE
(to boost color you may duplicate again the original and place on top in soft light mode)