Realistic heightmaps from coastlines & basic mountain positions- GIMP + Wilbur
So I've been making a map of a large region of a continent - the land of Totallynotmedievaleurope - starting with a hand-drawn coastline and locations of major mountain ranges.
Basically, the current map is color-coded with sea, lowlands, highlands, and three heights of mountains.
The problem is, I can't figure out how to turn this rough map into a realistic heightmap.
I really like the results from this tutorial: [Award Winner] Eriond - A Tutorial for GIMP & Wilbur
but I can't get the mountain chunks to blend together properly, and they don't match the shapes I came up with beforehand very well.
Are there any other good methods for generating a heightmap from this type of map?