How to smooth a curve

hi, while i was trying to do horizontal projection to extract plate area i faced a problem , how to smooth the curve in this picture: http://img811.imageshack.us/img811/8180/78807837.png

to be like this for further analysis: http://img88.imageshack.us/img88/559/41517039.png

i read about rank filter that may be make this but i don't know what is rank filters or how i can implement it i matlab pls help thx in advance