I think the saying, photoshop has a steep unlearning curve is going to apply here.
Forget how you worked previously. Gimp is not PS
Not going to put these screenshots in-line, have a look at them if you want.
WhiBal plugin - it is old (2007) a .8bf Might work with pspi or shellout and xnview but more trouble than it is worth.
looks like this http://imgur.com/ylQwqo2
Try the Gimp plugin g'mic http://www.gmic.eu which contains many filters that will accomplish the same result but in a different way.
Example http://imgur.com/tOcoRpR
Personally, I prefer the color curves, same section in g'mic. Get the HSV/HSL curves, pull them around to suit.
Forget how you worked previously. Gimp is not PS
Not going to put these screenshots in-line, have a look at them if you want.
WhiBal plugin - it is old (2007) a .8bf Might work with pspi or shellout and xnview but more trouble than it is worth.
looks like this http://imgur.com/ylQwqo2
Try the Gimp plugin g'mic http://www.gmic.eu which contains many filters that will accomplish the same result but in a different way.
Example http://imgur.com/tOcoRpR
Personally, I prefer the color curves, same section in g'mic. Get the HSV/HSL curves, pull them around to suit.