Is the radius of your strel function a constant value, or is it a variable?
In my experience with Coder, the app will correctly generate code if the arguments to strel are constants. Moreover, your structuring element must also be a constant in order for it to be used by the morphological functions (imopen, etc.).
So while this should work:
X = strel('disk', 5);
This will not:
X = strel(sStrelType, dStrelSize);
If you need variable-sized structuring elements, this can be a real pain, because you can't even make arrays of strels. I worked around those limitations by constructing several constant structuring elements and then using them in separate imtophat calls in the case branches of a switch statement. Very unpretty, but it works.
