[GIMP] Regional and Continental Coastlines Using Jitter

[Karro]

Okay, so it was suggested that I post something that discusses a little of the process I'm currently developing to create coastlines in GIMP, as an alternative to the random coastline method presented in RobA's famous Regional Map Tutorial. This little mini-tutorial assumes some familiarity with GIMP and with RobA's tutorial (what I know about GIMP, personally, I learned primarily from using that tutorial).

So, first off, what's the purpose? The idea behind this process is that sometimes you're working with a map where you want a little more control over the appearance of the land in the map than the use of the rendered clouds will produce. You might know that there are specific features you want to have--some of the possibly quite small--to appear in the coastlines and landforms of your final map. So... you need a method that will still help you produce some level of a realistic, fractalized appearance relatively quickly, but afford you that level of control.

Enter the Jitter feature.

I found that with judicious use of the a brush on Jitter can have the effect of roughing up a coastline and giving it an interesting appearance. Some times I go in with a very fine control, but here's a quick method that will produce results that you can then fine tune to reach the results you're looking for.

Step 1: The simple coastline

We start with a basic, simple-looking coastline.

Coastline Tut Step01.jpg

It already has several key geographic features that we want to maintain. We've got peninsulas, islands, and a narrow isthmus connecting two larger bodies of land. (Here, black is land, and white is the sea.) We want to preserve these features, but with a fractalized looking coastline.

To start, we need to invert the colors. (We'll want the black to represent the sea and white represent the land.) To do this, go to Colors > Invert.

Coastline Tut Step02.jpg

Step 2: Stroking the Selection
Beforfe we proceed, make a copy of the layer, in case we do something wrong, and want to revert to an earlier version. I do this after every step.

Next, we want to use the Wand tool to select the entire black region of the map. This will select everything that is part of the sea. After you have the black region selected, Invert the selection by going to Select > Invert. You will now have the entire white region selected. We select the black first then invert because if we tried to select one of the white regions with the wand tool, we'd miss several of the other white regions when we perform the Stroke action next.

Now, before "Stroking" the selection, we need to set up the brush we are going to use. Using the Brush tool set on circle 5 or 7, set the foreground color to either white or black. (I used Circle 5 set to black for this example, but you can use any shape you'd like.) Using white will build on the existing land, while black will carve out of it. I chose black because I had a couple inlets I liked that I wanted to preserve. Next, set the Jitter level. To do this, on the Paintbrush menu, check the box next to Jitter. You'll need a moderately high Jitter--the higher the Jitter, the more variation in where the brush will paint. Here, I used a setting of 1.75. I also set the spacing on the brush much higher than the default (here, 100). This helps to prevent a solid but squiggly line from being the result.

Finally, with our brush set up, we're ready to Stroke. Go to Edit > Stroke Selection. Make sure the check box/radial button for the Paintbrush is selected. This will ensure we use the settings on the brush that we just set up. Hit Okay and watch GIMP work it's magic.

Coastline Tut Step03.jpg

Before we unselect anything, our screen will look something like this:

Coastline Tut Step04.jpg

I'll proceed in the next post... but it may be a couple days before I can get this updated.

[Ghostman]

Interesting technique. Experimenting with custom brushes could lead to better looking results.

We select the black first then invert because if we tried to select one of the white regions with the wand tool, we'd miss several of the other white regions when we perform the Stroke action next.

There's no need for this: GIMP has a selection tool that will select all areas of same color. It's the next one to the right from the wand tool on the toolbox. Just click on any white area with this tool and you'll have every white pixel selected.

[Koren n'Rhys]

Really neat feature here. Is there a comparable bit in Photoshop? I'd like to give it a try if there is...

[Karro]

Interesting technique. Experimenting with custom brushes could lead to better looking results.

I imagine you're correct. At the moment, I don't have a lot of custom brushes, and the basic idea behind this is to make it available to others who are building on the basics. Theoretically, you should be able to take the idea and work with it to achieve results you like. But I can easily imagine some possible custome brush shapes that would produce very nice results.

There's no need for this: GIMP has a selection tool that will select all areas of same color. It's the next one to the right from the wand tool on the toolbox. Just click on any white area with this tool and you'll have every white pixel selected.

Hmm. Thanks for the tip. I haven't played with this tool, as yet. One thing about the wand tool, however, is it's ability to select some fuzzy areas and define how fuzzy, as well. Using the steps I used above actually picks up more of the white and whitish areas than I would if I'd selected just the white only. However, I'll check and see if the color select tool can help me achieve the same results.

Really neat feature here. Is there a comparable bit in Photoshop? I'd like to give it a try if there is...

I suspect there's at least a jitter feature on Photoshop; I don't know if there's a stroke selection tool as well (there probably is, but I'm not familiar enough with it to say so). The stroke selection, however, is primarily to help speed things up. The same technique can be used by hand painting with a jittery brush as well.

[Karro]

...Continuing on:
Step 3: Building up and tearing down
As I mentioned before, you can either start by stroking your selection with black or with white. Black will cut away from the land and white will add to it.

Either way, the key to the method is to alternate between black and white a little, using progessively smaller brushes.

So, next, we're going to build up on what we started last time. Before we proceed, unselect everything.

Then, let's set up our brush. You'll want the foreground this time to be the opposite of what you used the first time (this time I'll use white). You'll want to select a smaller brush size, but not too much smaller. To achieve the right balance, you may need to play with the scale setting of the brush. Again, you'll also want to increase the spacing setting. However, as you use smaller and smaller brushes, you'll want to increase the spacing less and less.

Because our last step already redefined our coast a little, we'll need to reselect the new coastline. Use the same procedure of wand-selecting the black region and inverting your selection. (If you don't invert when you wand-select the black ocean regions, when you stroke the selection, you'll also get little white bits, assuming you're using a white brush, on the outside edge of the map...)

Here's I'm setting up the brush:

Coastline Tut Step05.jpg

With your brush set up and your new region selected, you're ready to stroke the selection again.

Step 4: Wash, Rinse, Repeat

This step's fairly easy... just repeat Step 3, decreasing the brush size and changing the brush color, reselecting and re-stroking. After two or three iterations, you will probably reach something that is looking mostly good, if a bit rough around the edges.

Coastline Tut Step06.jpg

Coastline Tut Step07.jpg

Once you've done this, it's time to move on to:

Step 5: Cleaning Up a Bit

You may notice that there are a few relatively strange things going on. Our first attempt at using the jitter left a few circular holes close to our new coastlines. (Howbeit, your results may vary... which of course is the whole point.) Assuming those look as odd to you as they do to me, or if something else is bother you, it's time to clean that stuff up. In addition, I found the results a little too fractal-looking.

To clean up, I wand-selected the seas again, inverted to get the land, and then used a large brush set to white to fill in the erroneous-looking circles. This also cleaned up some of the over-fractalized edges.

Coastline Tut Step10.jpg

Once you've got this where you like it, you're ready to move on with the rest of RobA's regional map tutorial, or use this however else you'd like to use it.

If you're going to use this as the "land mask", again select the black oceans, invert, and go to Select > Save to Channel. Or, you can use the "edge detect" at Filters > Edge-Detect > Edge... (I prefer the "Gradient" setting if you do this) to get a line-drawing of the coastline. (You'll get a white line on black field... just go to Colors > Invert to turn it into a black line on a white field.)

Anyway, here I move on with the next few steps of RobA's tutorial, using the results I've created in this tutorial as the "land mask" channel.

Coastline Tut Step11.jpg

Final take-aways: this takes a little longer than the method RobA detailed in his tutorial, but gives you more control over the final result. It will take an artistic eye to find where the fractalizing goes too far and clean it up a bit, but it's easier than trying to draw all those squiggles by yourself.

I hope this method proves useful to you!