A simple method to create a blue(er) sky from the dull blue.
- Duplicate the layers so that you will end up three images ( Background, copy#1, Copy#2 )
- Desaturate the top layer ( copy#2)
- Set the blending mode to Grain Extract
- Merge this layer down with copy#1
- Set the blending mode of this merged layer to Grain Merge
- That's it. All Done !
Try these on non sky images as well