This paper presents an approach of forming high accuracy quasi circular structure elements which combines quasi circular structure elements formed with the dilation of the shortest line structure elements and those dilated with an unit structure element sequentially

which does not only to assure the high accuracy of quasi circular structure elements

but also save the related morphological computation greatly.We deduced the compatibility formulas under translation of the structure element and the conditions of satisfying the convex property of the quasi circular structure element

and proposed a fast algorithm of forming quasi circular structure elements sequentially.The quasi circular structure elements with radius from 0 to 59 are formed

whose absolute radius errors are less than 0 5.Finally

the optimal morphological skeleton algorithm are presented and exercised on 128×128 test image with time less ls on Pentium 166M PC.