FUNCTION lin_smooth,image,along_rows=along_rows,down_columns=down_columns

IF NOT (KEYWORD_SET(along_rows) OR KEYWORD_SET(down_columns)) THEN BEGIN
    MESSAGE,'Select either /ALONG_ROWS or /DOWN_COLUMNS!',/INFORMATIONAL
    RETURN,image
    ENDIF

tsize=SIZE(image)
IF tsize(0) NE 2 THEN BEGIN
    MESSAGE,'IMAGE must be an array!',/INFORMATIONAL
    RETURN,image
    ENDIF

@isitdos

IF KEYWORD_SET(along_rows) THEN temp=TRANSPOSE(image) ELSE temp=image

imsize=SIZE(temp)
ncols=imsize(1)

rn=INDGEN(imsize(2))
FOR ic=0,ncols-1 DO BEGIN                ; main loop to fix up one column
    coli=REFORM(temp(ic,*))
    res=ladfit(rn,coli,absdev=ad)
    minv=res(0)+res(1)*rn-ad
    maxv=minv+2.*ad
    ok=(minv LE coli) AND (coli LE maxv)
    bad=WHERE(ok EQ 0)
    alt=INTARR(imsize(2))
    alt(bad)=round(res(0)+res(1)*bad)
    coli=ok*coli+(1-ok)*alt
    temp(ic,*)=TRANSPOSE(coli)
    ENDFOR

IF KEYWORD_SET(along_rows) THEN temp=TRANSPOSE(temp)
RETURN,temp

END