In this tutorial, you will learn a simple way to export a 3D image as an STL by using Matlab. The functions you'll need to make the STL file in Matlab can be found in the 1st and 2nd link below, while a more in depth tutorial can be found in the 3rd link.
Okay: so let's get to it.
1. Save the above two functions into Matlab.
2. Make a 3D surface plot in Matlab.
For example, type in:
>> [X,Y] = meshgrid(-8,0.1:8);
>> R = sqrt(X.^2+Y.^2) + eps;
>> Z = sin(R)./R;
3. Use the surf2solid function which you downloaded earlier:
>> VariableName = surf2solid(X,Y,Z);
4. Use the stlwrite function that you downloaded:
*FileName is to be replaced with what you want to name your file
And there you have it, a nice simple way of exporting a 3D file from Matlab.