MEDIAN filter in IDL

PRO MEDIAN_FILTER
READ_GIF,'d:\Image\bird.gif',im
im1=im
sz=SIZE(im,/DIMENSIONS)
s=[0,0,0,0,0,0,0,0,0]
FOR i=1,sz[0]-2 DO BEGIN
FOR j=1,sz[1]-2 DO BEGIN
CO=0;
FOR k = i-1,i+1 DO BEGIN
FOR l = j-1,j+1 DO BEGIN
s[CO]=im[k,l]
CO=CO+1
ENDFOR
ENDFOR
im1[i,j]=MEDIAN(s)
ENDFOR
ENDFOR
WINDOW,0,XSIZE=sz[0],YSIZE=sz[0],TITLE='ORIGINAL IMAGE'
TV,im
WINDOW,1,XSIZE=sz[0],YSIZE=sz[0],TITLE='MEDIAN IMAGE'
TV,im1
END