; ----------------------------------------------------------------------
;  Fractional pixel summation with real row boundaries (fixed column).  
;  Sums up counts within boundaries.
;  rb1,rb2 = row boundaries 1 and 2 (lower and upper).
;  NOTE: You must check before calling that boundaries are within image[].
;  NOTE: You must check before calling that boundaries are within image[].
;  NOTE: You must check before calling that boundaries are within image[].
;  NOTE: You must check before calling that boundaries are within image[].
;
function nsxng_fractional_pixel_rb, nc, nr, image, rb1, rb2, icol

; Look at all relevant pixels. */
  imgsum=0.
;  for jj = round(rb1), round(rb2) do begin
;> check boundaries
  for jj = (round(rb1) > 0), (round(rb2) < (nr - 1)) do begin
; Edges of pixel. 
     pi1=jj - 0.5  
     pi2=jj + 0.5
; Column enclosure.
     if (pi1 gt rb1) then begin
        if (pi2 lt rb2) then begin
           rowfrac = 1.0        ; Fully enclosed. */
        endif else begin
           rowfrac = (rb2 - pi1) ;   Upper boundary in pixel. */
        endelse
     endif else begin
        if (pi2 lt rb2) then begin
           rowfrac = (pi2 - rb1) ;   /* Lower boundary in pixel. */
        endif else begin
           rowfrac = (rb2 - rb1) ;   /* Both boundaries within pixel. */
        endelse        
     endelse
     pixno = icol + (jj*long(nc))
     imgsum = imgsum + (rowfrac * (*image)[pixno])
  endfor
  return, imgsum
end