Original terrain 129 x 129
When zoomed closer to details, the low resolution
becomes visible as straight lines in the terrain
profile.
Expanded in Terragen to 513 x 513.
The shape stays pretty much the same as it was
in smaller detail, the straight lines are still visible.
However, you can now add more details e.g. by
generating a terrain with the option "add more details
in existing terrain".
Bi-linear interpolation (Picture Publisher).
Linear interpolation gives the same result as
expanding the terrain in Terragen.
You can add details now, but other interpolation
options probably give better results.
(Same as Triangle method in ImageMagick)
Bi-cubic interpolation (Picture Publisher).
Bi-cubic interpolation tends to accelerate the edges,
causing steeper slopes
(Hermit method in ImageMagick gives similar results.)
Spline interpolation (Picture Publisher).
Spline interpolation tends to soften the image.
In case of terrain, it causes softer slopes.
(Cubic method in ImageMagick seems to be very
similar to this.)
Mitchell (ImageMagick).
Mitchell is one of the more advanced interpolation
methods available on ImageMagick.
It gives a good combination of detail and soft slopes.
Lanczos (ImageMagick).
Another advanced interpolation meethod,
similar to Mitchell.
