I've been playing with creating mountains in gimp for scales of around 1px : 200m or bigger. The end results so far are not exactly as good as I want them to be, but I believe I got to a point where I can post the details of the process here and see if it sparks the interest of other people. Maybe we can get a better technique discussing it.
Before you start reading it, take a look at the end result, so you don't get disappointed after following through the tedious steps
Oh, and I should warn you that I suck at giving colour textures to mountains, so I just gave up and worked only the height map and bump mapping from it.
Let's go then.
- Select a the overall shape of the mountain [sshot-0], with a slightly irregular edge: pieces turned inside on the edge are great spots for the lines you'll draw later to make the spurs. Save this selection as "mountain mask"
- Create a new layer to be the base of your heigh map. We'll start with it's background at 50% gray. That gives you room to start meddling with the foothills after you're done with the spine and spurs.
- Fetch the "mountain mask" selection, and run a shaped (angular) gradient on it [sshot-1], from 50% gray to white. Select none, and then blur it just a ittle bit (I used gaussian blur 10 px) to make it blend well with the surroundings.
- Optional: You can play a little bit with curves now, to make the steepness of the mountain more to your liking. I made mine softer at the bottom and slightly steeper on the peaks. To be honest, it didn't affect the end result all that much [sshot-2]
- Hide the layer created above, let's call it "mountain shape".
- Create a new layer (let's call it "mountain spurs") and fetch the "mountain mask" selection again.
- Toggle the quick mask and let's play with it a little bit. What you'll do on it, is add lines descending from the peak to the base of the mountain. The best places for those to end are the places where the edge of the selection shift inwards. [sshot-3]
- Now you have the selection of the "spurs" made (you can save it so you are able to experiment with the intermediate steps if you're not satisfied with the result). Get back to selection, turning off the quick mask.
- Fill the selection again with the shaped gradient (angular) and have it's blend mode set to "Overlay". That'll make the shape of the "spurs" appear right above the overall shape of the mountain. To be honest, the mountain should look too "round" at it's peak by now, but we can fix that later, if we want to. [sshot-4]
- The base part of the height map is basically done. You can create a new layer (let's call it "mt height map") and copy-visible & paste the result so far in it.
- Now create a new layer with a tiny noise pattern. I used felimage's noise with size 3. Let's call this layer "noise" for now. I hide it, for it's just used as a displace map. [sshot-5]