How to generate a coarse mesh with snappyHexmesh
 

Hello everybody,
I use OpenFOAM 1.7.1 and I want to create a coarse mesh.
I need to create a mesh as input for open foam , but I am not able to generate it directly form the CT-images of my geometry, so I need to create an .stl file and then to use sHM to obtain a mesh.
The problem is that the .stl file has big dimensions (around 2e6 triangles, the images were 29x700x700 voxels) and with a high refinement of sHM the final mesh has even bigger dimensions. How could I set the parameters of sHMDict to obtain a coarse mesh or how could it be possible to directly convert image data to OpenFOAM readable files?
The images show a simplified example of the problem, A is the input image (e.g. from micro-CT). B ist the generated stl file (with iMorph). C shows an acceptable mesh for us (the resolution from the ct-scan is quite high)
Thanks in advance for any help.