I’m trying to solve the following exercise, but I think it’s not possible.

exercise problem

I guess I should perform a morphological opening to remove the line from Theta. I used the second to last structuring element, because the first doesn’t remove the horizontal line and second and last remove too much.

However, this second to last structuring element will as well remove some parts of the outer ring during erosion: image after erosion

Now I would perform dilation to finish the opening, but I think I would need the second to last structuring element horizontally mirrored to get the original image but without the horizontal line.

For Example for the pixel (1,3), (1,4), (1,5) and (1,6) (if (0,0) was in the top left corner): I would want to set each of this pixels to one, if the pixel above is one. So I need a structuring element like: [[0 1 0], [0 1 0], [0 0 0]]

Is there any other way to do this? Mirroring the structuring element doesn’t seem to be allowed here.

Thank you very much for your help.

Best regards.