Difference between morphological operations in matlab and simulink

Hey all,

I got some issues concerning the simulink morphological block erode . I'm using a 3x3 neighborhood the for the operation ( strel('square',3) is set at the function block parameters ). Everything is just working fine as long as the found object points aren't located at the image borders. If they're, the outcome of the block erode still contains the border points of the image, but actually due to the erode operation they should have been gone. Am I not fully understanding the block or what's my basic mistake here? If I'm using the matlab function bwmorph() for eroding the image, it gives me the desired outcome, which I'm actually expecting.

If it can't be fixed, I'll have to implement the operation as a matlab function block in simulink. If I do so, can anyone tell me about the runtime increse or decrease, that I'm getting? The final algorithm will be compiled to a rapid prototyping platform via a simulink interface.

Best regards!