This tutorial is simple and utilises the awesome tutorial by RobA.
Thread Link below
Making not so Random Coastlines in GIMP
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This tutorial is to get around an issue I noticed when using RobA's tutorial to do multiple landmasses of very drastically different size. I noticed that smaller islands tended to get very "bland" coasts, while the big continents got nice jags and inlets. So I have tinkered to figure out how to get those big maps with nice detailed small islands and nice big islands. Using this method should allow you to do it without pulling your hair out.
So, onto the mini-tutorial.
Begin using RobA's Random Coastline Map. Build the island, and stop once you have the "black jaggy island on black background". (Step 7 in RobA's Tutorial). Call the end result something like Island 1.
- Create a new transparent layer. Call it something like "Island 2" and set it to about 50% opacity (so you can see Island 1 poking through).
- Fill it with black. Draw your chosen shape for your island in white.
- Using the rectangle select select around the island.
- Gaussian blur that shape by 50+ px. A lot of my A4 (300ppi) have 100px Guassian blur or higher.
- Without removing the selection, create a new transparent layer (called Island 2 Noise). Move it below your blurred island shape and fill the selection with Render>Cloud>Solid Noise (Detail 15, X = 16, Y = 16). This should create a small noisy cloud with lots of detail in the selection area only.
- Set the layer mode of Island 2 to Overlay.
- Adjust the Colour>Threshold level until you're happy with the shape.
- Merge Island 2 Noise & Island 2.
- Set the layer mode of Merged Island 2 to Screen. Opacity should be returned to 100%.
You should now have a map with BOTH of your islands in a nice white shape against the black background. You can go in and edit either island by painting white or black onto the correct layer until you're happy with the results.
Repeat Step 2 until you have all the islands you need
Step 3: Complete RobA's Tutorial
Hopefully this will help people. I know it seems kinda simple and short, but it drove me nuts for a while until I had the chance to really tinker and play.