Heightmap Conversion with GDAL
GDAL (Geospatial Data Abstraction Library) can convert heightmaps into a format usable by 3d modelling software. Unlike QGIS it is not limited to 256 shades of gray (8 bit grayscale). Compare the two images above and note how much better the first model is because it was made using a heightmap with 65535 shades of grey.
Navigate to the directory containing your source file.
Obtain the MIN MAX heights by typing:-
gdalinfo -mm "source.tiff"
Then use those values to replace MIN MAX below:-
gdal_translate -of PNG -ot UInt16 -scale MIN MAX 0 65535 "source" "destination.png"
Thank you, KeePing
QGIS is free and can help you to create such a file.