Tutorial: GIMP fertilizer for greener grass

Just to get this out of the way first: yeah, I took a picture of the feet and legs of a group of marching band students waiting to perform. When I'm shooting an "event" such as this, I like to grab a few frames of unusual angles, background, or shots that show the setting in a different way. When I'm putting together end-of-year slideshows, and I use these shots for fill-in, transitions, title screen backgrounds, etc.


With that out of the way, here's my first attempt at a little GIMP tutorial, running through some post-processing steps I took, with particular emphasis on making the grass greener. At left is the original capture. Not bad, but I thought I could do a bit more with it.



My next step was a slight S-curve in the curves dialog, making the dark areas a bit darker (mostly the shoes) and the brighter areas really "pop". You probably can't see a difference in the thumbnail, but it should be noticeable if you click to see it bigger.



As I looked at the photo, I really wished that the grass were a bit greener (no pun intended). My first instinct was to make a new layer and fiddle with the green saturation in the Hue/Saturation dialog. No dice, it hardly had any effect on the grass at all. In fact, I started to get frustrated.
And then my brain finally caught on--the reason that the grass was ugly was that it was actually yellow! So, back into the Hue/Saturation dialog, this time fiddle with yellow instead of green. In fact, as you can see from the screen grab at left, I shifted all the yellow hue in the whole photo all the way over to green! I also upped the saturation and lowered the lightness, making it a deeper, fuller green overall. I can't promise that the settings in the screen grab are the exact ones I used in the final version below, but you'll have to see what works best for your photo anyway, it's not an exact science.

I was able to get away with a drastic change of hue since so much of the photo is free of any yellow. The change had no effect on the red/white/blue uniforms, and of course I was working on a separate layer, so I could use a layer mask to exclude the whole upper third of the picture where there's no grass. The only tricky part really was masking out the trombone slides, since they have a very yellow cast and were turned green also by my edit. I started off trying to select the trombones with the scissors select tool, but it was so slow and tedious that I ended up just painting in the required areas onto the mask with a small brush. The shoes also picked up a slight green cast in the highlight areas, and were excluded by the mask as well.

Here's the final result with the trombone slides restored to their glorious brassy lustre (click through to flickr to see it large):


Comments and questions always welcome!
--sdc