Grayscale erosion and Grayscale dilation simulink block

I was trying to find the minimum and maximum of the 3 x 3 neighbourhood for the video signal. I have used grayscale erosion and grayscale dilation simulation block. For some of the instances the maximum values is found to be less than the minimum value.

It would be great if example for using these two blocks posted in mathwork community.

Can someone tell me how to overcome this situation?

Thanks in advance