Interesting technique. I haven't gotten some good spurs out of it yet, but I've only dabbled with it a little. I can see how it should work.
I've got a few suggestions, if you like.
For coloring, I usually apply a gradient map from HSV(27,64,38 ) to HSV(36,36,65) to the height map (sshot-6.png in your tutorial). This ranges from medium-dark brown up to pale brown, then bump mapping adjusts it from there. I then mask the color layer and I'm off.
If you want, I explain this in my tutorial, Yet Another Mountain Tutorial Using GIMP.
To get the initial mountain area shape, I use RobA's 'Three Layer Sandwich' (TLS) technique. This saves me from trying to come up with a 'good squiggle', and can provide enough variation in the outline to work. For mountains, where I usually want a rougher outline than I do for landforms, I typically apply the noise layer in multiply mode rather than overlay.
For smoothing the ridged layer (the angular fill), I find that spreading things (Noise -> Spread) by about five pixels before Gaussian blur makes for a smoother height map.
Rather than overlaying your spur layer, you might try multiplying it. I can't say this'll work (I haven't gotten a good spur layer yet), but I think it may do something interesting for you.
I've got four layers of bump map on the attached images. First is ridge layer overlaid by noise ('low'), then ridge multiplied by noise ('high'), then multiplied by noise twice ('very high'), then multiplied by noise three times ('peak').
I ditched the spur layers I had for this one. Instead, I did a 20-pixel polar displacement using my high noise layer as the source for both inputs. (I normally have three noise layers at different noise frequencies, used throughout the image). This usually perturbs the shape quite nicely, as long as the control numbers are kept fairly low -- even breaking the range into multiple pieces. It gets a little weird finding a good mask for it, though :/
For foothills, you might explore the 'Shaped (spherical)' shape for the area rather than the 'Shaped (angular)' fill, then reduce the depth of the bump map. Look into making a very fuzzy work area and multiplying the noise layer on it; this might give you enough hills at high enough resolution. You may need to do it at a higher resolution and scale down. You might also explore using TLS with turbulent noise instead of nonturbulent noise (the default); this breaks the work area up somewhat. I'm somewhat disappointed by the regularity of the turbulence, though (seems to like to follow the eight cardinal directions, meh). The heightmaps that can be produced out of it are very rounded-lumpy, though, which can be nice.
Hmm, perhaps apply some displacement to the turbulence....
I took a shot at making some foothills... I'm not entirely happy with them, but I figured it was worth a try. I took the original mountain area and blurred it heavily (250 pixel radius), then did a multiply-TLS to get the region shape. Did a spherical shaped fill to get the basic height map, smoothed it (15 pixel spread and blur), then generated low and high height maps by overlaying and multiplying by my noise layer respectively. Bump mapped with low depth (linear, depth 10) using the height maps. Applied gradient color HSV(70, 51, 33) to HSV(40, 44, 39) to the hill layer and masked off with the hill selection channel. Frankly, I think my color choice here kind of sucks. Didn't particularly try to clean up the artifacts in the bump maps, normally I would.
Anyway, I hope this helps.
Keith
- kjd-20091204-001-displacement.png shows the mountains I got
- kjd-20091204-001-masked.png shows the mountains overlaid by the blurred 'starting area', there's a pretty good correspondence, I think.
- kjd-20091204-001-hills.png shows my first run at hills.
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