Document image segmentation to text lines is a critical stage towards unconstrained handwritten document recognition. Although morphological operations proved to be effective in processing machine-printed documents for several issues, similar methods for unconstraint-handwritten documents lack accuracy. We propose an efficient method based on binary morphology for text-line segmentation in such documents. The basic steps of our approach are: a) sub sampling and binary rank order filtering to enhance the text-line structures and b) applying dilations and (p,q)-th generalized foreground rank openings successively to join close and horizontally overlapping regions while preventing a merge in the vertical direction. The method tested on the benchmarking dataset of the ICDAR07 handwriting segmentation contest and show remarkable results.