Heightmaps in Photoshop:

Using Photoshop or a similar external editor to edit heightmaps offers some massive benefits over the ME tools.

If you don't know how to use Photoshop, your library should have a selection of books on it, or be able to get some. I recommend SAMS Teach Yourself Photoshop in 24 Hours, as it imparts a solid grounding in most aspects of the program.

First, you'll need to export your heightmap from the ME. Go to File > Export > Heightmap, then choose a location and name for it.

Painting Heightmaps:

Brief recap: White = high, black = low.

monoRAIL has made a rather handy image that correlates grey values with the ME Terrain Tool set levels. It certainly makes it easier to know what you're painting: external link to image

Once you have the heightmap open in Photoshop, you'll need to set the image up to show exactly where the play area is and where the border is. Guides are a good way to do this:

That heightmap measures 256*256 pixels, and the vertical and horizontal guides set at 64 and 192 pixels mark the 128*128 play area in the centre. Having guides also showing the exact centre is useful when you come to select, duplicate and rotate elements of the image, such as the flat topped hills you can see in the central area of the image above.

The ME is very friendly to exporting and importing heightmaps. Simply save it in Photoshop, then in the ME go to "File > Import > Heightmap" and select your file. The import shouldn't take more than a second or two, allowing you to quickly see the effects of your Photoshop work.

Handy Tricks:

Painting very fine gradiations seems almost impossible when the grey values are only a few points apart. However, if your graphics card allows it (and if it can run Dawn of War, it really should ;) ), then set the gamma way up in your graphics options and you'll be able to see exactly what you're doing at lower levels. Here's a shot of part of a coastline from a heightmap, showing it normally first, then with a simulated high gamma value:

Suddenly, very fine differences are highly visible and tunable. How high exactly you need to raise your gamma settings will depend upon your monitor.

Just to be clear: you won't be changing the brightness of the file, you'll be changing the brightness of your display. If you changed the brightness of the alpha map in order to see fine details, it would work in a similar way, but the bits of the map already at higher brightness values would cap out at 255, then be completely flat once you lowered the brightness and reimported the heightmap to the ME.

The blur tool is the equivalent to the ME smoothing tool, though you have to be careful about it bleeding outward and causing slopes to become gentler than you want them to be. Usually I find it better to do most of my editing in Photoshop then import the heightmap and use the ME smoothing tool to get rid of the jaggies.

A huge advantage Photoshop has over the ME tools is that you can mirror your terrain exactly, thus avoiding any players moaning about balance in your maps. Mirroring terrain horizontally or vertically is easy using the selection and transform tools. Mirroring it diagonally is a bit more obtuse, so here's an explanation:

Select the polygonal lasso tool, then, making sure that anti-aliasing and feathering are off, and that it will snap to guides, select two edges of the central play area, then join them diagonally across the middle. Copy and paste the selection into a new layer, then rotate it 90 degrees and perform one flip (Which way you rotate and flip depends on which half you selected).

Voila! It will leave a minor seam down the middle, but it's nothing you can't get rid of with the basic painting, blur and smudge tools.

Finally, the biggest advantage of using Photoshop is that you can save your heightmap as a PSD file, and use it to separate terrain features onto their own layers. This allows you to add, transform, and erase entire landforms without disturbing other parts of your heightmap.