;-------------------------------------------------------------
;+
; NAME:
;      IMAGSCL
; PURPOSE:
;      Procedure to find shift between two BBSO magnetograms,
;      to estimate the telescope image scale.
;      This is only good to the nearest whole pixel.
;
;      This procedure, given two images a1 and a2, 
;      displays a1 overlaid with a negative (pixels inverted)
;      version of a2.  The relative shift of a2 over a1
;      is controlled by moving the mouse and clicking.
;      When done, the relative shift is printed on the screen.
; CATEGORY:
;      IMAGE PROCESSING
; CALLING SEQUENCE:
;      imagscl,a1,a2,...
; INPUTS:
;      a1 = The first image.
;        type: array, any type.
;      a2 = The second image. 
;        type: array, any type.
; KEYWORD PARAMETERS:
;      NOBYTE = If present, then NOBYTE specifies that a bytscl
;        isn't to be performed.  It assumes that the input is
;        already in byte format.
; OUTPUTS:
;      Prints relative shift of one image over the other.
; COMMON BLOCKS:
; NOTES:
; MODIFICATION HISTORY:
;      J. Varsik,01 Nov, 1995 ---  Adapted from Cohl's FLICKER program.
;-
;-------------------------------------------------------------

pro imagscl,a1,a2,nobyte=nobyte,help=help

  ;Display idl header if help is required.
  if keyword_set(help) or n_params() lt 2 then begin
    get_idlhdr,'imagscl.pro'
    goto,finishup
  endif

  ;Print introduction.
  print,'     -------------------'
  print,'      Imgscl is running.'
  print,"       Type 'q' to exit. '
  print,'      Press a mouse button'
  print,'      to shift the image.'
  print,'     You may have to press'
  print,'    the mouse button again'
  print,"   after typing 'q' to exit.'
  print,'     -------------------'

  ;Byte scale images
  if (n_elements(nobyte) eq 0) then begin
    na1=bytscl(a1)
    na2=bytscl(a2)
  endif else begin
    na1=a1
    na2=a2
  endelse
  dev=getenv('IDL_DEVICE')
  dnc=!d.n_colors
  if (dev(0) eq 'SUN') then begin
      ;Scale Images
      na1=235*na1/255.
      na2=235 - (235*na2/255.)
  endif else begin
      na2 = 255 - na2
  endelse
  
  na2siz = size(na2)
  centerx = na2siz(1) / 2
  centery = na2siz(2) / 2
  nas = na1
  if (dev(0) eq 'SUN') then begin
    nas = na1 + na2 + 117
  endif else begin
    nas = na1 + na2 + 128
  endelse
  tv,nas
  while get_kbrd(0) ne 'q' do begin
;         read mouse position
    cursor,mx,my,/device
;         calculate image shift
    shiftx = centerx - mx
    shifty = centery - my
    if (dev(0) eq 'SUN') then begin
      nas = 117 + (na1 + shift(na2,shiftx,shifty))
    endif else begin
      nas = 128 + (na1 + shift(na2,shiftx,shifty))
    endelse
    tv,nas
    print,'shiftx = ',shiftx,' shifty = ',shifty
  endwhile

  finishup:

  return

end