Strange result morphological filtering with opening and closing

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Hi guys, i try to filter binarized image using closing and opening operation in morphological filtering. But, why the image completely damage ? (note: i have tried to invert the image). Is my kernel / structure element wrong ? Thanks.

invert the image :

Result

as an information, i use 3 x 3 disk structuring element

Mat k = getStructuringElement(MORPH_ELLIPSE,Size(3,3));

here is my opencv code :

Mat k = getStructuringElement(MORPH_ELLIPSE,Size(3,3));

morphologyEx( thresholdImg, openingImg, 3, k );
morphologyEx( openingImg, finalMorph, 2, k );