Some of the colour change will be down to adding a softlight layer in the GIMP. I think I have been a bit OTT on this shot and should have set the transparency to a lower figure. Easiest way to explain that technique is for you to do it yourself. Simply open a photo in the gimp. Go to the layers panel and right click and select duplicate layer. That will put another layer on top of the original one that will be selected. Set it’s layer mode to softlight and play with the opacity slider. On some shots it can give them a postcardy look - if that’s what you want or it can be very subtle. It can also be used selectively via new from visible and painting or layer masks etc. Much easier to do than some may think.
Messing with the colour channels alignment is more tricky. The GIMP has an auto levels button. It basically messes about with both the span and the alignment of the peaks in the histogram. It may also play with the position of the central slider on each channel. There is an old video on using this here.
On that shot I would probably play with each channel manually if needed after using auto and also reduce the output range to allow space for further work,
This one too - manually
The same thing can be done with the channel colour curves in RT but it’s a lot harder to do. Easiest way to show what I did to this shot is the pp3 file.
DSC09009.jpg.out.pp3 (10.1 KB)
I also use a curve to bring as much of the colour detail in the shot into jpg colour space. This is what came out.
Looking at the greens it needs more adjustment really but trying to do it completely with curves can be a truly tricky. This is why I requested gimp style levels in RT some time ago. It allows simple quick black and white point setting and mid tone contrast adjustment - easy on a curve too except when it’s applied differently to each colour channel. GIMP’s auto also usually does a decent job of making the adjustments.
As to why I did this - gut feeling down to extreme lighting. It can also be very useful in mixed lighting situations. The problem using the gimp is 8 bit. It usually results in gaps in the histogram. Not a problem unless further work needs doing - that is very likely to bring out banding. A problem for me as I take shots in any old conditions.
John