;
;  This function will add two disk images by means of interlacing every other
;  row.  Image1 will show all of the even rows and image2 will show all of the
;  odd one.  the final image is an interlacing of the two.
;

FUNCTION it_interlace, img1, img2

  sz1=SIZE(img1)
  sz2=SIZE(img2)
  temp=INTARR(sz1(1)>sz2(1),sz1(2)>sz2(2))
  temp_sz=SIZE(temp)
  temp_xcen=temp_sz(1)/2
  temp_ycen=temp_sz(2)/2
  img1_xcen=sz1(1)/2
  img1_ycen=sz1(2)/2
  img2_xcen=sz2(1)/2
  img2_ycen=sz2(2)/2

  x_offset=temp_xcen-(img1_xcen < img2_xcen)
  y_offset=temp_xcen-(img1_ycen < img2_ycen)

  ;print,'x_offset=',x_offset
  ;print,'y_offset=',y_offset
  ;print,'Size img1=',sz1(1),sz1(2)
  ;print,'Size img2=',sz2(1),sz2(2)
  ;print,'Size temp=',temp_sz(1),temp_sz(2)

  IF (sz1(1) LT sz2(1)) THEN $
   temp(x_offset:sz1(1)+(x_offset-1),y_offset:sz1(2)+(y_offset-1))=img1 ELSE $
   temp(x_offset:sz2(1)+(x_offset-1),y_offset:sz2(2)+(y_offset-1))=img2

  IF (sz1(1) LT sz2(1)) THEN $
    img1=temp ELSE img2=temp

  tmp=img1
  odd_arr=INDGEN(sz1(2) > sz2(2))
  even_arr=odd_arr

  ;odd_arr(where(odd_arr MOD 2 EQ 0))=0
  ;even_arr(where(even_arr MOD 2 NE 0))=0
  
  ;img1(*,odd_arr)=img2(*,odd_arr)
  img1(*,where(odd_arr MOD 2 EQ 0))=img2(*,where(odd_arr MOD 2 EQ 0))
  CATCH,error
  IF (error NE 0) THEN BEGIN
    print,'Found error in it_interlace'
    RETURN,img1
  ENDIF
  IF (sz1(1) LT sz2(1)) THEN BEGIN
      img1(where(img1 EQ 0))=img2(where(img1 EQ 0))
      img1(where(img1 EQ 128))=temp(where(img1 EQ 128))
  ENDIF ELSE BEGIN
      img1(where(img1 EQ 0))=tmp(where(img1 EQ 0))
      img1(where(img1 EQ 0))=temp(where(img1 EQ 0))
  ENDELSE
  image=img1
  RETURN,image

END