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Refining a Skybox from Terragen, By Jason Otto 02/27/2005
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Starting babble

Terragen is a free program available at http://www.planetside.co.uk/terragen/ which
is capable of creating realistic terrains for a variety of uses.  This tutorial 
will cover the steps needed to convert an environment in Terragen into a usable 
skybox for the Dark Engine.

This tutorial will assume that you've got a basic handle on the operation of 
Terragen.  Information regarding its use is available at the above URL.

This tutorial also assumes that you've read the basic tutorial on importing a 
skybox from terragen.  This tutorial will cover techniques to improve a 256 color
palette needed for the Dark Engine.
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Step One:

The individual frames from terragen should be combined into a large t shaped image.
This image is needed to assure a correct 256 color palette is applied to all the 
individual frames.
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Step Two:

Create two copies of the complete skybox image.  Reduce one image to 256 colors 
using an optimized octree and error diffusion.  Save the palette. Reduce the other
to 256 colors using an optimized octree and nearest color.
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Step Three:

Return both images to 16 bit color, copy the nearest color image and paste it as a
new layer over the error diffusion layer.  Adjust the layer opacity until an
acceptable blend is obtained.
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Step Four:

Merge the layers (flatten) and reload the error diffusion palette that was saved.
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Step Five:

Separate the image into individual parts and proceed as instruction in the general
terragen tutorial.
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Results:

By merging the two best color reduction methods into a single color reduction the 
best possible color reduction can be gained.  There seems to be no easy way to 
convert terragen skyboxes to 256 colors and retain the high level of detail they
possess.
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Application:

Improving any Terragen generated skybox for use with the Dark Engines 256 color
limits.